Authentic Writings

The most reliable sources are the authentic Epistles of Paul. Virtually every scholar holds to seven authentic Epistles: Romans, Galatians, Philemon, 1 Thessalonians, 1 and 2 Corinthians, and Philippians.

Disputed Writings

Beyond these seven undisputed epistles, there is scholarly debate over the Pauline authorship of both 2 Thessalonians, Colossians, and Ephesians. Approximately 60 percent of scholars hold to an authentic Thessalonians and Colossians, and about 15 percent or so hold to an authentic Ephesians.

See Paul Foster's article "Who Wrote 2 Thessalonians: A Fresh Approach to an Old Problem" JSNT 35:2 (2012) in favor of 2 Thessalonians' authenticity.

For the authenticity (and a catalog of arguments in favor and against authenticity), see Harold Hoehner's Ephesians: An Exegetical Commentary.

For the authenticity of Colossians, see James D.G. Dunn The Epistles to the Colossians and Philemon.

Dubious (?) writings

Few scholars today hold to the authenticity of the Pastoral Epistles. Largely speaking, they presume an ecclesiastical structure that seems better situated in the late first century, as well as making reference to later events, different vocabulary, etc. However, Luke Timothy Johnson's The First and Second Letters to Timothy is probably the most articulate defense of their authenticity.

Sources of Disputed Value

The Acts of the Apostles, the fifth book in the New Testament and one of the longest ones, may or may not be a good source for the life of Paul. A maximalist position, such as that advocated by Colin Hemer in his The Book of Acts in the Setting of Hellenistic History supports the idea that Luke, the evangelist, was a companion of Paul, and therefore the information about Paul in Acts is reliable, independent testimony about Paul. However, this is countered by the minimalist position, held by Richard Pervo and much of the Acts Seminar, that Luke the evangelist was using a collection of Paul's letters in the early second century. See Acts and Christian Beginnings: The Acts Seminar Report, ed. Dennis B. Smith.

Further Reading

There are two major biographies of Paul today.

Jerome Murphy O'Connor's Paul: His Story. and Douglas Campbell's Framing Paul: An Epistolary Biography.