[8] In 1984, he announced to his friends, family, and co-ministers that he had become an atheist,[9] and appeared on AM Chicago (hosted by Oprah Winfrey) later that year on a show about "kicking the religion habit".

He is the current co-president with his wife Annie Laurie Gaylor of the Freedom From Religion Foundation, an American freethought organization that promotes the separation of church and state.

[14] Barker is co-host of Freethought Radio, a radio program based in Madison, Wisconsin for atheists, agnostics, and other freethinkers that began in 2006 and has included interviews with Richard Dawkins, Sam Harris, Steven Pinker, Christopher Hitchens, Philip Pullman, Daniel C. Dennett, Ron Reagan, Julia Sweeney, and Michael Newdow.

[15] Barker has appeared on dozens of national television and radio programs to discuss and debate issues related to atheism and the separation of state and church.

He has discussed nativity scenes on government property,[16] the campaign against a Mother Teresa stamp,[17] prayer in public schools,[18] and has appeared on Oprah Winfrey, The O’Reilly Factor, Tucker Carlson, Laura Ingraham, Phil Donahue, Hannity & Colmes, Maury Povich, Good Morning America, Sally Jessy Raphael, and Tom Leykis, as well as many international television and radio shows.