Hahn received his B.A. in 1979 from Grove City College in Pennsylvania with a triple major of theology, philosophy, and economics (magna cum laude). He obtained his M.Div. (summa cum laude) from Gordon-Conwell Theological Seminary in 1982. In May 1995, he was awarded a Ph.D. in systematic theology from Marquette University (Phi Beta Kappa). His dissertation, entitled Kinship by Covenant: A Biblical Theological Analysis of Covenant Types and Texts in the Old and New Testaments, is a significant example of contemporary covenantal theology.

Hahn started out as a Presbyterian minister and theologian with years of ministry experience in congregations of the Presbyterian Church in the United States of America or PC, and Professor of Theology at Chesapeake Theological Seminary.

As a young theologian, Scott Hahn was convinced that the Catholic Church was in error, and boasted of having converted some Catholics into embracing a purer Christianity. His conversion began when he and his wife became convinced that contraception was contrary to God's law. He continued to study various issues relating to salvation, faith, and good works, as well as the Protestant doctrine of sola scriptura.

According to his book Rome Sweet Home, a key factor behind his conversion is his research on what he saw as the key to the Bible: the covenant. This is a sacred kinship bond that brought people into a family relationship. God established a series of covenants and the new covenant established by Jesus Christ is an establishment of a worldwide family. He believes that Jesus and the apostles used family based language to describe his work of salvation: God is Father, Christ is Son and the firstborn among brethren, heaven as a marriage feast, the Church is the spouse of God, Christians as children of God.

This new family, according to Hahn, is headed by Christ and the Pope is his "prime minister" to whom he has given the keys of the kingdom, a process that he believes is also present in the Old Testament. Hahn tries to show that the Catholic Church, whose head is called "Holy Father", is the worldwide family described by the Bible and that the Protestant doctrines of sola fide and sola scriptura are not biblical because they are not found in the Bible. In his view, the Bible stresses charity and works as necessary for saving faith (i.e., justification) and therefore salvation. He also points to the Church as the "pillar and the bulwark of the truth" (1 Tim 3:15).

Scott Hahn converted to Catholicism at Easter 1986 in Milwaukee, Wisconsin. Many people, using his wife's words, have started to call him "Luther in reverse", since a large number of Protestant pastors and Bible scholars have followed suit in converting to Catholicism.

Hahn's wife, Kimberly, had a similar conversion at a slightly later date, entering the Catholic Church at Easter 1990 in Joliet, Illinois. Rome Sweet Home describes their process of conversion together.

In Ordinary Work, Extraordinary Grace, he narrated the influence of Opus Dei in his conversion, and what made him feel that Opus Dei was his specific calling within the Catholic Church: (1) its members' devotion to the Bible, (2) its ecumenism, since Opus Dei was the first Catholic institution to welcome non-Catholics as cooperators, (3) the upright lives of its members, (4) they were ordinary people, who lived theology, (5) holy ambition: "a devout work ethic", (6) the practice of hospitality in answering his questions, (7) prayer: "They made time for intimate prayer every day."

Hahn founded and is currently the President of the St. Paul Center for Biblical Theology, a Christian research center and think tank committed to the promotion of biblical literacy among the Catholic laity and biblical fluency among Catholic clergy. Some of his projects include online and parish-based Bible studies, a book series, pilgrimages, and a scholarly journal, Letter and Spirit. He is also the founder and director of the Institute of Applied Biblical Studies.

A popular speaker, Hahn has given over 800 talks in the US and other countries on theological and biblical topics related to the Catholic faith and appears regularly on the Eternal Word Television Network (EWTN). He has also written numerous books (see list below) and is the co-editor of several volumes of the Ignatius Catholic Study Bible.

Since 1990, Hahn has served as Professor of Theology and Scripture at the Franciscan University of Steubenville. He was awarded Doctor of Humanities — honoris causa, by the Pontifical University of Puerto Rico in 2004.