Clark made his first recording in 1952 as a member of the Hambone Kids, who scored an R&B hit with the song "Hambone." In 1953, he joined an R&B group called the Goldentones, who later became the Kool Gents and were discovered by Chicago radio DJ Herb Kent upon winning a talent competition. Kent got the Kool Gents signed to Vee-Jay record label, subsidiary Falcon/Abner. The group changed its name once again, to "The Delegates," and recorded for Falcon/Abner in 1956.
Clark embarked on a solo career in 1957 and over the next four years landed several moderate hits, two of which ("Just Keep It Up" and "Hey Little Girl") reached the top 20 on the Billboard Hot 100). His biggest single, "Raindrops," a power ballad augmented by heavy rain and thunder sound effects and Clark's swooping falsetto, hit in the spring of 1961 and became his biggest hit, soaring to number two on the pop chart (behind only Gary U.S. Bonds' "Quarter to Three") and number three on the R&B charts. The narrator of the song tries to convince himself that the tears he has cried since his love left him are raindrops, since "a man ain't supposed to cry." "Raindrops" sold over two million copies and remains a staple on oldies radio station playlists to this day, and has also been covered by several other artists in the years since, including David Cassidy, Tony Orlando and Dawn, and most notably Narvel Felts, who took the song to number 30 on the country chart in 1974. Clark himself recorded an updated version of "Raindrops" in 1973.
However, Clark's biggest hit was also his last. The follow-up to "Raindrops," "Don't Walk Away From Me," was a flop, and he made the pop charts in America only twice more, with "I'm Going Back to School" (1962) and "Crossfire Time" (1963). By the time "Crossfire Time" came out, Clark had moved from Vee-Jay to the Constellation label. Though he continued to record for Constellation through 1966, none of his records charted. Clark had a brief revival in 1975 when his song "Ride a Wild Horse" became a surprise top 30 hit in the UK Singles Chart, becoming his first chart hit in the UK since "Just Keep It Up."
Afterward, Clark performed mostly on the oldies circuit. By the late 1980s, he was in dire straits financially, living in a welfare hotel in Toccoa, Georgia. Despite suffering a stroke in 1987 that left him partially paralyzed and with a mild speech impediment, he continued to perform until his death on 7 December 1990, in Smyrna, Georgia, from a heart attack at the age of 52.