Thomas was raised in and around Houston, Texas, graduating from Lamar Consolidated High School in Rosenberg. Before his solo career, he sang in a church choir as a teenager, then joined the musical group The Triumphs. During his senior year he made friends with Roy Head of Roy Head and The Traits. The Traits and the Triumphs held several Battle of the Bands events in the early 1960s.
In 1966, B.J. Thomas and The Triumphs released the album I'm So Lonesome I Could Cry (Pacemaker Records). It featured a hit cover of the Hank Williams song "I'm So Lonesome I Could Cry". The single sold over one million copies and was awarded a gold disc. The follow-up single, "Mama", peaked at No. 22. In the same year, Thomas released a solo album of the same name on the Scepter Records label.
Thomas came back to achieve mainstream success again in 1968, first with "The Eyes of a New York Woman", then five months later with the much bigger "Hooked on a Feeling", which featured the sound of an electric sitar and was first released on the album On My Way (Scepter Records). "Hooked on a Feeling" became Thomas's second million-selling record. A year later Butch Cassidy and the Sundance Kid featured Thomas performing the Bacharach/David song "Raindrops Keep Fallin' on My Head", which won the Academy Award for best original song that year and hit No. 1 on the Billboard Hot 100 in January 1970. Sales of also exceeded one million copies, with Thomas being awarded his third gold record. The song was also released on an album of the same name. Other hits of the 1970s were "Everybody's Out of Town", "I Just Can't Help Believing" (No. 9 in 1970, covered by Elvis Presley), "No Love at All", "Mighty Clouds of Joy", and "Rock and Roll Lullaby".