Do Catholics subscribe to the "once saved, always saved" doctrine that many evangelical Christians believe in?

I can answer as an evangelical¹, Bible-believing, Catholic Christian.

This question is asking about Soteriology.

The question's parameters suggest that being evangelical and Christian a person must not be Catholic; they would also suggest that if you are Catholic, you are neither evangelical nor Christian.

The teachings of the two separate and distinct perspectives rests on, by necessity, the authority given to the Church. Issues, when understood as the Catholic version of infused righteousness requiring priests and sacraments for initial justification, and a life long pursuit of sanctification towards glorification, is a logical progression.

By removing that Christ-given authority, those who do so (having placed themselves in a position opposing ministerial priesthood) are forced by a logical progression to reject all things that the priesthood stands for. Imputed righteousness , a progression of doctrines stripping orthodox Christianity away one piece of doctrine at a time, results in OSAS beliefs now accepted by may Fundamentalists across the sea of Christian belief.

Where the two faith perspectives differ: absolute assurance

The issue is one of absolute assurance of salvation. The quoted verses separated brethren often use to support this notion of absolute assurance is vague and does not take into account those scriptures which show that absolute assurance is counter to biblical teachings.

1 Corinthians 10:12 Therefore let any one who thinks that he stands take heed lest he fall.

I often hear Fundamentalists state that they know that they stand, and they can never fall. I suggest to you that this and countless other scripture addresses the very topic of OSAS and opposes it. The tradition of suggesting that you are certain of your salvation reminds me of the self righteousness of the Pharisee's Prayer (From Luke 18: 9-14)

Thank you Lord for Making me a Jew, Thank you lord for making me a Pharisee and not a gentile sinner

The Lord is anything but unclear when he says:

Matthew 7:21-23 "Not every one who says to me, 'Lord, Lord,' shall enter the kingdom of heaven, but he who does the will of my Father who is in heaven. On that day many will say to me, 'Lord, Lord, did we not prophesy in your name, and cast out demons in your name, and do many mighty works in your name?' And then will I declare to them, 'I never knew you; depart from me, you evildoers"

The Lord goes on with this pattern in reverse, but one thing is for certain: those who are being saved did not have assurance and those that believed themselves to have assurance were left wanting. Those who did not know their destination were saved; the only Christians who fit this description are the Catholics.

The bottom line on OSAS and Catholics

Do Catholics subscribe to OSAS doctrine of the Fundamentalists?

Absolutely not.

Why? Because it is not biblical, not historical, not orthodox and not feasible. The Doctrine of OSAS minimizes the critical importance of faith, leading many into sin. The fear of sin and the consequence of sin has been shifted to an expectation of an inability not to be sanctified, and an excuse for living outside the Grace of God with a false OSAS safety net that does not exist.

Catholics put their faith and hope in Jesus Christ. This is all we have and we can be quite comfortable with that hope. To claim absolute assurance, however, is to judge ourselves: this is a thing even Saint Paul would not do.

1 Corinthians 4:3-5 But with me it is a very small thing that I should be judged by you or by any human court. I do not even judge myself. I am not aware of anything against myself, but I am not thereby acquitted. It is the Lord who judges me. Therefore do not pronounce judgment before the time, before the Lord comes, who will bring to light the things now hidden in darkness and will disclose the purposes of the heart. Then every man will receive his commendation from God.

It is God alone that will Judge us: the just for Glory and the unrighteous for punishment. The sin of presumption is a common one, put your faith in God without presumption. We must be Christians inwardly.

¹ It is necessary to define the terms, especially "Evangelicalism." It has nothing to do with evangelism. One must possess the Truth in order to share it. Now, possessing the quality of evangelism -- spreading the Good News -- via the Pillar and foundation of the Truth, which is the Church, is how the Catholic Church perceives evangelizing. The use of the label "Evangelical" as a Noun -- rather than a adjective advocating the spread of the gospel -- is a Label empty of any significance other than cultural identity.

Richard McBrien (1936 – 2015) was a Roman Catholic priest and Professor of Theology at the University of Notre Dame. He wrote:

A Christian is not only a radically social human person in whom God is present in grace and who is, at the same time, prone to acting against the divine presence [this is how Roman Catholicism, in McBrien’s account, sees all human beings]. A Christian is also a person who has moved up to a different level of human consciousness. The Christian is one who believes in Jesus Christ and whose whole life is shaped by that belief. The process by which the human person moves up to that level of consciousness is called conversion.’

Catholicism, p 1005

Regarding the possibility of 'un-conversion' he wrote:

The basic orientation toward God is called the fundamental option, the state of being converted to the Kingdom of God. Only an equally fundamental reversal of that choice for God is sufficient to cancel out the original act of conversion. Such a reversal is a rare occurrence for one who is sincerely oriented toward God.

Catholicism, p1006

So from McBrien's interpretation of Roman Catholic theology, there is no unbreakable bond between the soul and the Lord in this present age.

A few points I'd like to mention as well: When you confess your sins to a priest, the priest is acting as a representative of Christ to forgive your sins. He has the power to forgive sins that are confessed by a truly repentant Christian in the same way that someone you give power of attorney can execute your will. The attorney is given power to act on your behalf under special conditions, and we wouldn't think of him as having the same authority as you.

Similarly, you should look into the Catholic conceptsof baptism by blood and baptism by desire. The former applies to people who wanted to become Christians but who were martyred before baptism for refusing to relinquish their beliefs. Baptism by desire is a similar concept for those who wanted to convert and otherwise never had the chance before they died. All this is simply to say that Catholic teaching on salvation is very nuanced and complicated. There are so many little rules and exceptions that "once saved always saved" is a hard criteria to answer. One possible answer to your question could lie with perfect contrition, which is where you are sorry for your sins because of the fact that you know they offend God. Perfect contrition is sufficient to absolve minor sins and even grave ones if you are sincere in your desire to seek confession when it is possible. Of course, baptism is required for full salvation, so perhaps a baptized Catholic with perfect contrition could fit the definition of once saved always saved? http://www.vatican.va/archive/ccc_css/archive/catechism/p2s2c2a4.htm

Paragraph 1452 covers perfect contrition if you are interested.

(Posted on mobile, sorry about any typos that arise)

Actually Catholics would have to assent to the statement that "once saved, [one is] always saved" (I'll refer to this belief as "OSAS" for short). The difference is in when Catholics believe one is saved.

The Evangelical Protestants whom you refer to generally seem to believe that one is saved once one deliberately turns to God and accepts Jesus as Lord and Savior:

The Bible clearly tells us that at the moment we first believed, we were given the seal of the Holy Spirit as a deposit guaranteeing our inheritance. This confirms that our salvation is assured (Ephes. 1:13-14). Paul confirmed this in 2 Cor. 1:21-22 adding that God has taken ownership of us and it is He who makes us stand firm in Christ. The Bible also says that we're saved by faith alone, not by works (Ephes. 2:8-9). So the basis for our salvation is belief, not behavior, and it's guaranteed right from the start. This is possible because all the sins of our life were forgiven at the cross (Colossians 2:13-14).¹

(emphasis added; see source notes below)

Catholics, on the other hand, believe that one is not actually saved until one's individual judgment (the particular judgment) at death:

Death puts an end to human life as the time open to either accepting or rejecting the divine grace manifested in Christ. The New Testament speaks of judgment primarily in its aspect of the final encounter with Christ in his second coming, but also repeatedly affirms that each will be rewarded immediately after death in accordance with his works and faith. The parable of the poor man Lazarus and the words of Christ on the cross to the good thief, as well as other New Testament texts speak of a final destiny of the soul—a destiny which can be different for some and for others.

(Catechism of the Catholic Church, paragraph 1021; emphasis added)

In Catholic belief, one is justified (that is, given grace by God enabling one to be saved) at Baptism:

The Most Holy Trinity gives the baptized sanctifying grace, the grace of justification:

• enabling them to believe in God, to hope in him, and to love him through the theological virtues;
• giving them the power to live and act under the prompting of the Holy Spirit through the gifts of the Holy Spirit;
• allowing them to grow in goodness through the moral virtues.

(Catechism of the Catholic Church, paragraph 1266; emphasis added)

This sanctifying or justifying grace is something one always has (its status is like the OSAS view of how one has salvation):

Incorporated into Christ by Baptism, the person baptized is configured to Christ. Baptism seals the Christian with the indelible spiritual mark (character) of his belonging to Christ. No sin can erase this mark, even if sin prevents Baptism from bearing the fruits of salvation.

But it, in itself, is not what saves. Rather, one's cooperation with God as a consequence of sanctifying grace, and with the help of further graces received as a consequence of baptism, is what God allows to save us:

The merit of man before God in the Christian life arises from the fact that God has freely chosen to associate man with the work of his grace. The fatherly action of God is first on his own initiative, and then follows man’s free acting through his collaboration, so that the merit of good works is to be attributed in the first place to the grace of God, then to the faithful. ...

Since the initiative belongs to God in the order of grace, no one can merit the initial grace of forgiveness and justification, at the beginning of conversion. Moved by the Holy Spirit and by charity, we can then merit for ourselves and for others the graces needed for our sanctification, for the increase of grace and charity, and for the attainment of eternal life.

(Catechism of the Catholic Church, paragraphs 2008, 2010; bolded emphasis added)

¹ Taken from the website GraceThruFaith.com, which describes itself as

a non-denominational, non-church, Christian ministry dedicated to providing believers with a deeper understanding of the whole counsel of God through His revealed word.

The site describes its belief framework with respect to OSAS:

We believe that our salvation is laid up in heaven, free for the asking, granted to everyone without condition or prejudice, out of the incomparable riches of God’s grace. ...

We believe that all who ask will receive, all who seek will find, and to all who knock the door will be opened. It is our Father’s will that all who look to His Son and believe in Him will be saved.

We believe that once this relationship is sought and granted it can never be revoked or relinquished. While the Bible encourages us to live our lives in a manner pleasing to God, our salvation is not contingent upon maintaining certain standards of behavior.

A baptized Catholic would understand "accepting Jesus" as meaning professing the (Catholic) Faith; he would interpret "repenting of one's sins" as receiving absolution from a priest in the sacrament of penance, and thus being in a state of grace (the state of not having the stain of mortal sin on his soul). If he were to die in a state of grace, he would either go straight to heaven, or, if he still has temporal punishment remaining for his already forgiven sins, he would go to purgatory for awhile and eventually go to heaven. Since one can fall out of the state of grace by committing mortal sin, or by committing numerous venial sins that predispose one to eventually commit a mortal sin, one is not guaranteed to be saved "once and for ever" just because one once "accepted Jesus and repented of one's sins."