I think the strongest evidence is that of crucifixion practice of the Romans would be that no one would be allowed to or possibly could survive a Roman crucifixion (see On the Physical Death of Jesus Christ in Journal of Medical American Association. This article is available online).

Now, this requires to explanation to respond to the suggestion that he could have already repented and been baptized before even being put on the cross.

Matthew and Mark both report a plurality of those being crucified to revile Jesus.

“Even the robbers who were crucified with Him reviled Him” (Matthew 27:44)

“Even those who were crucified with Him reviled Him” (Mark 15:32)

It is also reported that there were only 2 crucified with him. Luke reports that only one reviled him. Later, one of them defends Jesus, which is the topic of the question. (I'll ads all these references later). What is the best explanation? I take my discussion primarily from this apologetics article defending against the contradiction.

It is quite reasonable to say that one of them repented during his time on the cross (this interaction with Jesus, observing His prayers and offering of forgiveness, etc might be compelling, especially at this point in time and if he had no previous interaction with him, such as if he was in prison). If he repented during his time on the cross, and he certainly wouldn't be able to be baptized before death, then he would be unbaptized. This is the more common belief, that he repented during his time on the cross. In fact, I hadn't heard anyone suggest otherwise before; it may be due to the strangeness of saying someone who is a Christian is later being executed for being a "robber".

Other explanations may be that Matthew and Mark are using a literary device when making the plurality, or saying that they are contradictory, or some redactional value perhaps to have the repentent robber in Luke's Gospel.

Are we perhaps forgetting that God knows the heart of every man; the penitent thief on the cross alongside Jesus, you can be sure, would have been eager to have been baptized in water if only he could have been, but he couldn't be, as he was nailed to a cross, couldn't get down, and wouldn't survive; the thief on the other side of Jesus, just mocked, Jesus, and would certainly not have been obedient to be baptized in water even if he could have been.

Why is it that many so called 'Christians' are so quick to use the example of the thief on the cross, to excuse their own disobedience to be baptized in water, rather than be like the eunuch who said "See, here is water, what is there to prevent me from being baptized," few people seem to wish to use this example, many people wish to use the example of the thief on the cross who was willing, but unable to be baptized.

The witness of loving obedience to be baptized in water as commanded by God, means a lot to God, not so much to us it seems; the thief had an excuse for not being baptized, he was nailed to a tree, and would hang there until he died, a reasonable excuse I would suggest, but what is our excuse? God is listening, and watching, if the excuse is just, He will know, but if we out of pride simply refuse to be baptized as we approach God for His gift of grace towards us, His forgiveness of our sins, then we have much more in common with the thief that mocked Jesus, and make null and void God's plan for our salvation - as Jesus Himself has said to the Jews that refused water baptism.

It does matters, it is serious.

I agree that the thief very likely had heard the testimony of Jesus prior to his arrest and crucifixion, he may well have been baptized in water, we cannot know at present - however, it breaks my heart that people use this event as a reason not to be baptized in water, using the event as an excuse (as I have said, why do they not use the eunuch as their example) - it speaks volumes about their claim of love for Jesus, and desire for forgiveness and a new start, only last week I spoke to a minister who was voicing the very same excuse, "The thief on the cross wasn't baptized," meaning therefore we are all okay, safe and sound in our disobedience says he. However, Jesus said "The one who really loves Me, is the one who keeps my commandments," all of them, not just baptism - 'Faith' - repentance, obedience to be baptized with sincerity, in water, and to sincerely seek baptism with The Holy, which will be attested to by God Himself Spirit, He can refuse you see, if we are not sincere, and then our faith is all about behaviour, behaviour, behaviour, behaviour, behaviour, behaviour, behaviour, behaviour, behaviour - continued faith is revealed in continued righteous behaviour. A lot of 'Christians' seem not to know, or perhaps care to know, that the Christian Faith is all about behaviour, behaviour Satan wants to corrupt. It is as simple as that, both baptisms are essential, baptism in water should be a humbling act of obedience, our refusal is our own proud rebellion, baptism with The indwelling Holy Spirit, is the point at which we come to know Christ (The Anointing) within us - "At that time (The upper room when The Holy Spirit comes upon them), you will know that I am in My Father, you are in Me, and I am in you, - "If a man is in Christ, he is a new creation....," If Christ is not IN YOU (at that time you will know that I am in My Father, you are in Me, and I am in you - this why Paul used those words - "If Christ is not in you..), you are none of His," Jesus said we "Must be born again."

The simple Truth of this message from Jesus and the disciples is all but lost, and it distresses me to know it, breaks my heart.

John baptized with water, but Christian baptism began after Pentecost, following the commandment of the risen Christ to "go forth and make disciples of all nations, etc". In baptism, the minister of the sacrament (who could be a lay person in case of emergency) represents Christ and transmits the fruits of Christ's sacrifice on the cross (i.e. redemption) through the sacrament. Christ's promise of salvation to the good thief is the reality of which baptism is an efficacious symbol. So no, you don't need to be baptized if you are being crucified alongside Christ and he promises you salvation. For the rest of us, baptism is a sacramental way of conveying the salvation which the good thief received directly, without intermediary. Because he was there.

Note: I'm RC.

Jesus Saves: He has the power to do this by fiat

Which renders the question of baptism moot.

From the Apostle's Creed (shared by many Christian denominations)

He suffered under Pontius Pilate, was crucified, died, and was buried.
He descended to the dead. On the third day he rose again.
He ascended into heaven, and is seated at the right hand of the Father.
He will come again to judge the living and the dead.

This is a case where he pronounced judgment on one of the living. Your question covers one instance. While Jesus was on Earth, exercising His power as the one who administers Final Judgment fits his being The Son. He had the power while on Earth to forgive sins. (Matthew 9:6)

But that you may know that the Son of Man has authority on earth to forgive sins" he then said to the paralytic, "Rise, pick up your stretcher, and go home."

Another instance of making a similar ruling for one of the living is in Luke 7:50. After sharing the parable of the two debtors with Simon, Jesus tells the woman that she is saved.

But he said to the woman, "Your faith has saved you; go in peace."

Nobody questions her salvation since Jesus decreed it. Whether or not she was previously baptized (as a follower of Jesus, she may well have been baptized by John the Baptist) is moot because Jesus Saves.

Let's look at the thief on the cross again. He professes his faith that Jesus is the Messiah, the Anointed one.

39 Now one of the criminals hanging there reviled Jesus, saying, "Are you not the Messiah? Save yourself and us." 40 The other, however, rebuking him, said in reply, "Have you no fear of God, for you are subject to the same condemnation? 41 And indeed, we have been condemned justly, for the sentence we received corresponds to our crimes, but this man has done nothing criminal." 42 Then he said, "Jesus, remember me when you come into your kingdom." 43 He replied to him, "Amen, I say to you, today you will be with me in Paradise."

It is a fair reading of that interaction that it is the same kind of ruling as in Luke 7:50 - the Thief's (professed) faith grants him salvation (his faith saves him).

Now that Jesus has ascended, he judges the dead, not the living, and Christian practice from the earliest church includes baptism as a means of professing their faith that Jesus is the baptizeds' hope of salvation. (If there is a denomination of Christians who do not profess their faith if Jesus as a part of Baptism, I am not aware of it).

Does the narrative of the thief on the Cross mean Baptism isn't necessary?

No; Jesus no longer walks among us as a man as he did then. He now administers judgment in heaven, having left instructions (the Great Commission) for the baptism of, and sharing the gospel with, the whole world.

_{He does something similar in Mark 5:34 and Luke 17:19: "your faith has healed you" however whether that is simply the physical healing, or a deeper spiritual healing, is arguable. (I've seen arguments both ways ... )}

There is no evidence that the thief was not baptized, except the silence of the scriptures...

On the other hand, the evidence that the thief may well have been baptized under the authority of Jesus Christ is as follows:

1. Much of Judea was baptized by John the baptist.

4 John appeared, baptizing in the wilderness and proclaiming a baptism of repentance for the forgiveness of sins. 5 And all the country of Judea and all Jerusalem were going out to him and were being baptized by him in the river Jordan, confessing their sins. -Mark 1:4-5

4 Now John wore a garment of camel's hair and a leather belt around his waist, and his food was locusts and wild honey. 5 Then Jerusalem and all Judea and all the region about the Jordan were going out to him, 6 and they were baptized by him in the river Jordan, confessing their sins. -Matthew 3:4-6

Now of course when it says all of Jerusalem and Judea and all the region of the Jordan this may be a bit of hyperbole, but needless to day a significant number of Jews were being baptized by John.

2. Even more Jews were Baptized by Jesus!

Whatever large number of people were baptized by John, Jesus baptized more!

25 Now a discussion arose between some of John's disciples and a Jew over purification. 26 And they came to John and said to him, “Rabbi, he who was with you across the Jordan, to whom you bore witness—look, he is baptizing, and all are going to him.” -John 3:25-26

1 Now when Jesus learned that the Pharisees had heard that Jesus was making and baptizing more disciples than John... -John 4:1 ​

Also note that baptism was how Jesus was making disciples of the Jews, similar to how he later instructs the apostles to do to the nations.

19 Go therefore and make disciples of all nations, baptizing them in the name of the Father and of the Son and of the Holy Spirit, 20 teaching them to observe all that I have commanded you. -Matthew 28:19-20

3. The thief of the cross displayed advance knowledge and faith in Jesus

“Jesus, remember me when you come into your kingdom.” -Luke 23:42

So given the likely very large number of Jews that were disciples baptized under the authority of Jesus, it is very possible that the thief on the cross was one of their number who had somehow gotten lost along the way given his seemingly advanced knowledge and belief in the identity of Jesus. This advanced faith in Jesus and the Gospel of the Kingdom indicates prior belief and interaction with either Jesus or his disciples.

Given that evidence that the thief may have been a baptized believer...

The evidence that he was not baptized is simply the silence of the scriptures.

Remember that the original Greek didn't use punctuation, and whatever you see in English versions has been added by the translators, often based on their previous understanding of tradition.

In this case, the appropriate place for a comma in that verse could have been inserted after, rather than before the word "today".

That would give it a completely different meaning. Compare:

• Verily I say unto thee, today shalt thou be with me in paradise.
• Verily I say unto thee today, shalt thou be with me in paradise.

How can we know which one is the correct interpretation?

One way is to observe the use of sentence structure in Greek. The thief's statement was "remember me when thou ...". A balanced response to that would match the "when" with the "today". That is, Jesus tells him that there is no need to wait until the Kingdom, that He can tell him right away.

An even stronger indication that this is what was actually meant is given by matching more explicit facts given elsewhere in the Bible. In John 20:17, Jesus says "I am not yet ascended to my Father" and this is after the Resurrection. He had just spent three days and three nights in the grave, so the thief couldn't possibly have been in paradise with Jesus on the "today" mentioned during the crucifixion.

The comma goes after "today", Jesus lied, or the Bible contradicts itself.

All we know for sure then is that Jesus assured the thief that he would be with Jesus in "Paradise" when Jesus has his Kingdom.

Some denominations teach that the Kingdom of God is here on Earth now, so I can't speak for them. But others believe that the Kingdom will be here on Earth for a thousand years following Christ's return. At the end of that Millennium, there will be a second resurrection of those that died without ever being offered salvation (Rev 20:5), the vast majority of mankind. It is then that they will live in God's Kingdom, as physically resurrected people, and then that the vast majority of them will be saved. Finally, those few that still reject God, along with those in the third resurrection (Rev 20:13), who had previously died after rejecting salvation, will all be destroyed in fire (Rev 20:15), turned to ashes under our feet (Mal 4:3).

That second general resurrection into the Kingdom is when the thief will be given his first chance at salvation. It is then that he will be baptized.

And, assuming the other thief hadn't previously accepted God's holy spirit and then later rejected it, he too will be there.

The OP has not ask for a particular denomination to give answers to his question so I will bring in my reformed/calvinist belief. Although this will be just my thoughts from scripture, there are some things that God's word does not share with us perhaps leaving us with different meanings to encourage us at different points or growth with our walk with Him.

Scripture is clear that we must hear His word before we can believe.

"so then faith comes by hearing the word of God. ( Roman's 10:17)

"How shall they call on him in whom they have not believed? And how shall they believe in him of whom they have not heard? And how shall they hear without a preacher? (Romans 10:14)

This indicates that the thief had indeed heard the word. Whether he had believed or not has not been answered for us but all indication is that he had not been born again when he was on his cross with our Lord Jesus. Perhaps the thief has heard John the Baptist or even Jesus in the past.

Now this is where it will get sticky for many of you but please bear with me.

(Romans 8:30) " Moreover those He predestined, them he called; and whom he called, them he also justified: and whom he justified; them he also glorified".

This is a speculative question as with all answers should be considered. Of course my answer comes from a calvinist point of view.

This thief was predestined from the foundation of world. God knew him intimately before conception. Our Lord made and took this thief as His own on His death bed! The thief confessed Jesus Christ as Lord and Saviour in his final hours. Our Lord heard his pleas as God had planned from the very beginning. Wow, what a Saviour!

This gives each and everyone of us a hope even for our loved ones that have not yet been called. We must "wait on the Lord."

There is no proof for if the thief was or was not baptized.we can only believe what Gods word tells us and what His Holy Spirit lays upon our hearts. Thank you for your time and giving me a box to stand on.

Since the OP mentions that the thief's baptismal state is used by some to draw conclusions about salvation, I will do more than answer the title question.

As others have said, we are not told one way or the other whether the thief had undergone baptism of any sort. We do know that he died prior to the commandment being given under the Christian dispensation; his legs were broken so that he would suffocate on the cross and thus he died long before Pentecost. Any baptism he had undergone would have been done under the Law, which was still in effect at the time this exchange took place. However, it is impossible to arrive at any reliable conclusion. We simply are not told.

Call me crazy, but I hold the position that if we need to know something in order to be saved, God will tell us.

From this I conclude that the thief's baptismal state has no bearing on our salvation.