Active primarily during the 1950s through 1970s, Collins was instrumental in helping create the Bakersfield sound of the country music genre. He enjoyed a string of hits during the mid-1950s including "It Tickles" and "Watcha Gonna Do Now." He also wrote several songs for other artists, including "If You Ain't Lovin' (You Ain't Livin')," which originally became a top 10 hit for Faron Young in 1954 and became a No. 1 hit by George Strait in 1988.
After several years in the ministry, Collins returned to recording. In 1965, he had a comeback hit with "If You Can't Bite, Don't Growl." In the 1970s, he wrote several hits for Merle Haggard, including the No. 1 hits "Carolyn" and "The Roots of My Raising." In 1981, Haggard recorded a biographical tribute to Collins called "Leonard," the title referring to Collins' real name.
Collins remained active in the songwriting business. He died March 14, 2000, in Ashland City, Tennessee.