There was just no mention of God.

Billed as Louisiana’s first atheist service and titled “Joie de Vivre: To Delight in Being Alive,” it was presided over by Jerry DeWitt, a small, charismatic man dressed all in black with slick, shiny hair.

“Oh, it’s going to be so hard to not say, ‘Can I get an amen?’ ” he said with a smile, warning people that this was going to be more like church than they might expect. “I want you to feel comfortable singing. And I want you to feel comfortable clapping your hands. I’m going to ask you to silence your cellphones, but I’m not going to ask you to turn them off. Because I want you to post.”

As Mr. DeWitt paced back and forth, speaking with a thick Southern accent, his breathy yet powerful voice occasionally cracked with emotion. The term may be a contradiction, but he is impossible to describe as anything but an atheist preacher.

Mr. DeWitt acts so much like a clergyman because he was one.

He was raised Pentecostal in DeRidder, La., a small town near the Texas border. In 2011, after 25 years as a preacher, he realized he had lost all connection to the religious point of view that had defined most of his life. He left the church and found himself ostracized in his hometown and from his family. Since then, Mr. DeWitt, 43, has become a prominent advocate of atheism, giving lectures around the region and providing an emotional counterpoint to more academic atheist exponents like Richard Dawkins and Christopher Hitchens.

With Sunday’s service — marking the start of Community Mission Chapel in Lake Charles, which Mr. DeWitt called a full-fledged atheist “church” — he wanted to bring some of the things that he had learned from his years as a religious leader to atheists in southern Louisiana.