He received his undergraduate degree in Applied Math at UCSD in 1972 and went on to get a J.D. at the University of San Diego. He worked as an attorney practicing civil law in the early 1980s.
Leaving Mass one Sunday in 1979, he found anti-Catholic tracts on the windshields of the cars in the church parking lot. He wrote his own tract in reply and distributed copies of it at the Fundamentalist church responsible for the tract. That was the start of what has become the country’s largest lay-run apologetics and evangelization organization.
Keating's book Catholicism and Fundamentalism was based on a 1988 series that ran for 30 weeks in The Wanderer. It is a perennial bestseller for its publisher, Ignatius Press.
In 1988, Keating changed careers and went into apologetics full time. He gives talks throughout the United States, and also engages in public debates with Protestants.
He has been a columnist for The Wanderer, the National Catholic Register and the Canadian Catholic Review. He has also acted as expert on EWTN's Questions and Answers forum. His avocations include mountain biking, hiking, backpacking, "Jeeping", flying, and browsing Internet forums.
A 2004 complaint to the Internal Revenue Service by the pro-choice organization Catholics for a Free Choice led to an IRS investigation of Catholic Answers that Keating described as costly and onerous. As a result, he formed a new organization with a separate 501(c)(4) tax status, called Catholic Answers Action, that continued publishing his Voter's Guide for Serious Catholics. This instructs readers not to vote for candidates who would vote for legalisation of any of five "non-negotiable" issues (abortion, euthanasia, embryonic stem cell research, human cloning, and gay marriage). Some diocesan lawyers in California and Wisconsin had earlier attempted to suppress this voting guide in 2004. No official endorsement of this guide has been offered by the United States Conference of Catholic Bishops or any official Church body.
- Catholicism and Fundamentalism: The Attack on "Romanism" by "Bible Christians" (Ignatius Press, 1988)
- What Catholics Really Believe (Servant Publications, 1992)
- Nothing but the Truth: Essays in Apologetics (Catholic Answers, 2000)
- The Usual Suspects: Answering Anti-Catholic Fundamentalists (Ignatius Press, 2000)
- Controversies: High-Level Catholic Apologetics (Ignatius Press, 2001)
- Holy War, Just War: Islam and Christendom at War (Chronicles Press/The Rockford Institute 2007)