Stuart Lee Williamson was born May 14, 1933, in Brattleboro, Vermont, seven years after his brother Claude, who would become one of the most respected bebop pianists on the West Coast. In 1949, at sixteen, Stu followed his brother west to Los Angeles, and the two spent the next decade circling the same small pool of Hollywood recording studios, Hermosa Beach clubs, and touring big bands. They appear together on record often enough that discography credits routinely confuse them, and Claude is the pianist on both of Stu's Bethlehem leader dates.

Williamson's apprenticeship was in the big bands. He joined Stan Kenton in 1951, moved to Woody Herman's Third Herd for 1952 and 1953, and returned to Kenton for a second stretch in 1954 and 1955, where he was featured as a soloist on Kenton Showcase: The Music of Bill Holman (Capitol H526) and played the trumpet section on Contemporary Concepts, cut in July 1955. He also worked for Billy May and Charlie Barnet in the same period. The reading demands of that circuit gave him something most small-group soloists never developed: enough power and accuracy to hold down a lead chair in a full brass section, which is why arrangers kept calling him for the next fifteen years.

By the mid-1950s he was one of the busiest horns in Southern California. He recorded repeatedly with Howard Rumsey's Lighthouse All-Stars, including Vol. 5: In the Solo Spotlight (1954) and Vol. 6 (1955) on Contemporary, and worked intermittently with Shelly Manne between 1954 and 1958, appearing on four consecutive Shelly Manne & His Men albums for Contemporary: Vol. 4: Swinging Sounds (recorded January and February 1956), More Swinging Sounds: Vol. 5 (July and August 1956), Vol. 6: "Concerto for Clarinet & Combo" (1957), and The Gambit (1958). Alongside those came dates with Charlie Mariano, Lennie Niehaus, Bud Shank, Bob Cooper, Bill Perkins, Duane Tatro, and Zoot Sims, the last of whom used him on both trumpet and valve trombone.

His own catalog is small and concentrated in a three-year window. The quintet session of January 18 and 20, 1955, in Los Angeles, with Mariano on alto, Claude Williamson on piano, Max Bennett on bass, and Stan Levey on drums, produced the 10-inch Bethlehem LP Sapphire (BCP 1024) and, two years later, its expanded 12-inch replacement Stu Williamson Plays (BCP-31), with three additional titles. In between, on January 13 and 16, 1956, he cut the septet album simply titled Stu Williamson (BCP-55), adding Bill Holman on tenor, Jimmy Giuffre on baritone, Leroy Vinnegar on bass, and Mel Lewis on drums to the Mariano/Claude Williamson core. In July 1957 he made two records in Hollywood in the same month for Mode: A Jazz Band Ball (First Set) (MOD LP #110), co-credited with trumpeter Jack Sheldon and featuring Williamson on valve trombone alongside Don Fagerquist and Bob Enevoldsen, and the Pepper Adams Quintet (MOD LP #112), the recorded leader debut of baritone saxophonist Pepper Adams, on which Williamson took the trumpet chair beside Carl Perkins, Leroy Vinnegar, and Mel Lewis just before Adams left the coast for New York.

From 1959 onward the work shifted decisively toward the studios. He was in the trumpet section of Terry Gibbs's big band on Launching a New Band (Mercury, 1959) and on the live The Exciting Terry Gibbs Big Band, taped at The Summit in Hollywood in January 1961. He recorded with Marty Paich on The Broadway Bit and behind Paich's orchestra for Mel Tormé, Ella Fitzgerald, and Anita O'Day, played trumpet on Dizzy Gillespie's The New Continent (Limelight, taped in Hollywood in September 1962), and turned up on Astrud Gilberto's 1965 Verve album and Lalo Schifrin's Music from Mission: Impossible in 1967. A final co-billed jazz date, credited to Bud Shank with Maynard Ferguson, Stu Williamson, and Bob Enevoldsen, appeared on Crown in 1963.

Williamson stopped playing in 1968, at thirty-five, and never came back. He struggled with drug addiction for most of his adult life, including the years after he left music, and he passed away in Studio City, California, on October 1, 1991, at fifty-eight. His two Bethlehem albums have stayed in circulation through Fresh Sound reissues, including Stu Williamson Plays: The Bethlehem Years (1989) and the 2005 compilation The Trumpet Artistry of Stu Williamson, and the Mode sessions returned on V.S.O.P. vinyl in the mid-1980s and on Japanese CD in 1989.

Williamson worked in the leaner, more transparent idiom that Los Angeles arrangers favored in the 1950s, but he was not a cool-school miniaturist: he had a full, round tone and built solos out of long melodic phrases rather than the clipped figures common on the coast, and he could push a big-band lead part with the clarity the section needed. Shelly Manne, who used him for four straight Contemporary albums, called him "a wonderful trumpeter and valve trombonist," singling out his reading, his time, and his sound. His doubling was genuinely equal, which was rare; on Bud Shank's The Saxophone Artistry of Bud Shank, Art Pepper's The Artistry of Pepper, and Anita O'Day's Trav'lin' Light he is credited on trombone rather than trumpet, and Bill Perkins and Zoot Sims hired him for both horns at once. Because he retired at thirty-five with only two albums under his own name, most later assessments reach for the same word: underrated.