Though primarily known as a single act, Slim's bands included the "Red River Rangers", "The Trailriders" and "The Trailsmen." Country music favorites Kenny Roberts and Dick Curless (The Tumbleweed Kid) were members of the Red River Rangers and the Trailriders, respectively. In 1946, Slim signed with Continental Records in New York City, at the urging of yodeler Elton Britt. He made his first 78 RPM recording that same year. The songs he recorded at Continental were largely traditional cowboy and folk tunes, along with a few Wilf Carter songs and some originals, often co-written with Pete Roy. Clark stayed with the label until 1957, followed by associations with several independent labels. He cut four singles for Doc Williams' Wheeling label in 1953 and later made an album for the Canadian Arc label. In 1965, Clark recorded a few excellent albums for Palomino records.
During his very active career, Slim has recorded over 50 78's, 40 45's and over 25 albums. Copies of his old 78's are in the Library at the Country Music Hall of Fame and Museum, and have become collector's items. Slim also appeared coast-to-coast on both the NBC network and the ABC network on different jamborees. He was featured on Folk Music USA. Slim performed western music for 70 years. He gained popularity throughout the United States, Canada, Australia, New Zealand, and Europe with only a handful of appearances outside his life-long New England base. After a partial retirement in the early 1970s, he recorded for Palomino Records, and played many festivals during the summertime.
Slim won the World Yodeling Championship in 1947 and was inducted into the Yodeler's Hall of Fame, along with Jimmie Rodgers, Elton Britt, and Wilf Carter. He was a member of the Western Music Association's Hall of Fame. He is represented in the Walkway of Stars at the Country Music Hall of Fame and Museum in Nashville. In November 2000, he was posthumously inducted into the Cowboy Hall of Fame.
In 1945, Slim began spending his summers in Maine and in 1952 he became a resident of Maine, where he met and married his wife Kathy. Slim had two children. His son, Wilf Clark, still performs and is a recognized yodeler with the Misty Mountaineers. He also had a daughter named Jewell.
In retirement, most of his time was spent painting. He became recognized for his lifelike paintings of outdoors scenes -- one of his most popular paintings being that of a Lombard Log hauler.
Slim died in his adopted hometown of St. Alban's, Maine.