In 1964, the Beefeaters, an L.A. folk trio comprised of guitarists Jim (later Roger) McGuinn, David Crosby, and Gene Clark, released a single, "Please Let Me Love You"; after its commercial failure, they decided to add a bassist and drummer to their lineup. Their producer, Dickson, suggested Hillman for the bass position; although he had never picked up the instrument before, thanks to his bluegrass background he was able to quickly develop his own unique, melodic performance style. After the addition of drummer Michael Clarke, the quintet renamed itself the Byrds. At their label's insistence, they cut their first record with sessionmen, which meant that Hillman and Clarke sat on the sidelines during production; the resulting single, a jangly cover of Bob Dylan's "Mr. Tambourine Man," was a tremendous hit that marked the birth of the folk-rock form.
During the mid-'60s, the Byrds ranked as one of the most successful and influential American pop groups, issuing a string of massive hits like "Turn! Turn! Turn!," "Eight Miles High," and "So You Want to Be a Rock 'n' Roll Star" along with acclaimed albums like 1967's Younger Than Yesterday and 1968's brilliant The Notorious Byrd Brothers. Internal strife dogged the band, however, and by late 1967, only Hillman and McGuinn remained from the original roster. At about the same time, Gram Parsons entered the picture, and in December 1967, McGuinn invited him to join the group as a jazz pianist for a planned project embracing the history of American popular music. However, Parsons' mastery of country soon became the sessions' dominant focus, much to Hillman's delight, and the album the Byrds ultimately recorded, 1968's Sweetheart of the Rodeo, became the blueprint for all country-rock efforts released in its wake.
The Desert Rose Band proved to be Hillman's most commercially successful post-Byrds project; their first LP, an eponymously titled 1987 outing, generated a pair of Top Ten country hits in "Love Reunited" and "One Step Forward," which peaked at number two. Released in 1988, "He's Back and I'm Blue" topped the country charts, as did "I Still Believe in You," from the album Running. Two other singles from the record, "Summer Wind" and a cover of John Hiatt's "She Don't Love Nobody," reached the Top Five. The follow-up, 1989's Pages of Life, was also highly successful, with two more Top Ten hits, "Start All Over Again" and "Story of Love." Subsequent releases like 1991's True Love and 1993's Traditional failed to achieve the same degree of popularity, however, and after one final LP, Life Goes On, the group called it quits in 1994.