Did Pontius Pilate follow God's Plan?

Throughout the Bible we see that God uses not only people, but circumstance and even Nature to affect his plans. When God uses people to fulfill his needs, God uses that person's natural tendencies to do his will. God does not change a person to fit the situation; he changes the situation to fit the persons natural tendencies.

Take the following Scriptures for example:

All Scripture is quoted from the King James translation.

Exodus 4:21 And the LORD said unto Moses, When thou goest to return into Egypt, see that thou do all those wonders before Pharaoh, which I have put in thine hand: but I will harden his heart, that he shall not let the people go.

In order to harden Pharaoh's heart God did not change Pharaoh's egotism, he only used that Ego to facilitate his plans.

This excerpt from David Gusik's commentary on the Bible further explains this:

2. (19-23) God tells Moses how events will unfold in Egypt.
And the Lord said to Moses in Midian, "Go, return to Egypt; for all the men who 
sought your life are dead." Then Moses took his wife and his sons and set them on a 
donkey, and he returned to the land of Egypt. And Moses took the rod of God in his 
hand.And the Lord said to Moses, "When you go back to Egypt, see that you do all 
those wonders before Pharaoh which I have put in your hand. But I will harden his 
heart, so that he will not let the people go. Then you shall say to Pharaoh, 'Thus
says the Lord: "Israel is My son, My firstborn. So I say to you, let My son go that 
he may serve Me. But if you refuse to let him go, indeed I will kill your son, your 
firstborn."' "
a. The men who sought your life are dead . . . I will harden his heart: God knew 
Moses was safe in Egypt, and so eased his mind from this anxiety; but God also knew 
that He would harden Pharaoh's heart, and that it would take the death of the 
firstborn before Pharaoh would agree to release the children of Israel.
i. Sometimes, it says that God hardened the heart of Pharaoh (Exo. 4:21). Sometimes 
it says that Pharaoh hardened his own heart (Exo. 8:15). Sometimes it says simply 
that Pharaoh's heart was hardened, without saying who did it (Exo. 7:13).
ii. Who really hardened Pharaoh's heart? We might say that it was both God and 
Pharaoh; but whenever God hardened Pharaoh's heart, He never did it against Pharaoh's
will. Pharaoh never said, "Oh, I want to do what is good and right and I want to 
bless these people of Israel" and God answered, "No, for I will harden your heart 
against them!" When God hardened Pharaoh's heart, He allowed Pharaoh's heart to do
what Pharaoh wanted to do - God was giving Pharaoh over to his sin (Rom. 1:18-32).
iii. "God does not harden men by putting evil into them, but by not giving them 
mercy." (Augustine)

We find other great examples of God using natural inclination throughout the Story of Joseph in Genesis chapters 37 through 50. (I have not quoted them here for the sake of brevity.)

God used the natural tendencies of Jacob (his favoritism of Joseph) to create jealousy among his brothers. He used the bothers natural tendency toward revenge to affect the sale of Joseph to the Ishmaelites,

Genesis 37:27-28 Come, and let us sell him to the Ishmeelites, and let not our hand be upon him; for he is our brother and our flesh. And his brethren were content. Then there passed by Midianites merchantmen; and they drew and lifted up Joseph out of the pit, and sold Joseph to the Ishmeelites for twenty pieces of silver: and they brought Joseph into Egypt.

God used not only Potiphar's inclination to utilize Joseph's talents for his own personal gain, but also his position under Pharaoh to place Joseph in Pharaoh's prison.

Gensis 37:36 And the Midianites sold him into Egypt unto Potiphar, an officer of Pharaoh's, and captain of the guard.

I could go on about Potiphar's wife, and all the others whose natural inclinations he used to get Joseph in position to save the Hebrew Nation, but you can glean it out for yourself.

I could also go on indefinitely describing God's use of Samuel, David, Saul, and so many others, but since you asked about Pilate There are some thing you need to consider about Pilate and his natural tendencies to assess God's use of Pilate to complete his plan for Jesus death on the cross.

Pilate was not a champion of the Jew's and was in fact disdainful of them. Pilate had in fact already been chastised by Rome for his harsh treatment of the Jews.

Luke 13:1 There were present at that season some that told him of the Galilaeans, whose blood Pilate had mingled with their sacrifices.

David Gusik elaborated on this scripture:

1. (1-5) Jesus uses two recent disasters to drive home a point.
There were present at that season some who told Him about the Galileans whose blood 
Pilate had mingled with their sacrifices. And Jesus answered and said to them, "Do  
you suppose that these Galileans were worse sinners than all other Galileans, because
they suffered such things? I tell you, no; but unless you repent you will all
likewise perish. Or those eighteen on whom the tower in Siloam fell and killed them,
do you think that they were worse sinners than all other men who dwelt in Jerusalem?
I tell you, no; but unless you repent you will all likewise perish."
a. The Galileans whose blood Pilate had mingled with their sacrifices: We don't have
a record in secular history about the specific incident mentioned here. But there is
a similar incident before the ministry of Jesus, Pilate wanted to build an aqueduct
from the Pools of Solomon to the city of Jerusalem. To pay for it, he demanded money
from the temple treasury, money that had been dedicated to God - and this outraged
the people. When the Jews sent a delegation to beg for their money back, Pilate sent
into the crowd soldiers dressed as common people, and at a certain signal they took
out daggers and attacked the people asking for the money.
i. This doesn't seem to be the same incident mentioned here, but it shows how 
completely consistent it was with the character of Pilate to slaughter some Galilean
Jews on their way to sacrifice to the Lord in Jerusalem.

God did not change Pilate's natural tendencies to be tyrannical in order to see his plan to its conclusion, rather he used Pilates tyrannical nature to do so. It was purely Pilates own decision to allow the Crucifixion of Christ.

We don't yet know. Even if God used Pilate as an instrument in his plan of salvation, we don't know enough details about the rest of Pilate's life. Whatever else he might have done or not done, if he truly repented before his death, he would have gone to heaven; if he did not repent, he would not have.

Yes Pilate carried out God's plans but his actions were still sinful. In Acts 2:23 Peter explained that the crucifixion was God's plan carried out by the Jewish and Gentile leaders:

But God knew what would happen, and his prearranged plan was carried out when Jesus was betrayed. With the help of lawless Gentiles, you nailed him to a cross and killed him. (Acts 2:23, NLT)

It's important to remember that just a few days earlier, Jesus had warned his disciples:

Matthew 18: 7:

Woe unto the world because of offences! for it must needs be that offences come; but woe to that man by whom the offence cometh!

Yes, having Jesus be betrayed and killed was part of the plan, but that does not mean that the specific persons who played a part in bringing it about were not guilty of some very serious sins anyway.