Carl Hilding Severinsen was born in Arlington, Oregon, on July 7, 1927, and has been called Doc since childhood, after his father, the town's only dentist. He wanted to play trombone, but his arms were too short for it and the local music store had none, so he started on cornet with lessons from a neighbor. He was playing in a school band at seven, won a state trumpet contest at nine and a national music-teachers' contest at twelve, and at fourteen auditioned for Tommy Dorsey and was turned down. His boyhood idol was the trumpeter and bandleader Harry James. Before finishing high school he was hired to go on the road with the Ted Fio Rito orchestra.

In the mid-1940s he moved through a run of touring dance bands, among them those of Charlie Barnet, Dorsey, Benny Goodman, Sam Donahue and Noro Morales, and he was a featured soloist with Dorsey. He served in the Army during World War II. In 1949 he settled in New York as a staff musician at NBC, where he accompanied Steve Allen, Eddie Fisher, Dinah Shore and Kate Smith, played in the original band for Tonight Starring Steve Allen and was the soloist on its closing theme. He left with Allen in 1957.

Studio work in New York made him one of the busiest trumpeters in the big-band jazz of the late 1950s and early 1960s. Discogs credits him on trumpet on Chris Connor's Witchcraft (Atlantic, 1959), Ruth Brown's Late Date with Ruth Brown (Atlantic, 1959), George Russell's New York, N.Y. (Decca, 1959), the Concert Jazz Band album Gerry Mulligan Presents a Concert in Jazz (Verve, 1961) by Gerry Mulligan, Dizzy Gillespie's Perceptions (Verve, 1961), Bob Brookmeyer's Gloomy Sunday and Other Bright Moments (Verve, 1961), Gary McFarland's The Jazz Version of "How to Succeed in Business Without Really Trying" (Verve, 1962), the Stan Getz and McFarland collaboration Big Band Bossa Nova (Verve, 1962), the Milt Jackson Orchestra's Big Bags (Riverside, 1962), where he plays on three tracks, and the big-band tracks of Jimmy Smith's Bashin' (Verve, 1962). He is also listed on dates for Dinah Washington, Anita O'Day, Gil Evans and Tito Puente.

The television job that defined him came back in 1962, when bandleader Skitch Henderson asked him to return as first-chair trumpet on The Tonight Show Starring Johnny Carson. Milton DeLugg led the band for a short stretch after Henderson left, and in 1967 Severinsen took over as leader of the NBC Orchestra, the house band better known as the Tonight Show Band. He held the baton for twenty-five years, until Carson's last broadcast in May 1992, and became one of the most visible bandleaders in the country: gaudy, brightly colored stage clothes, running jokes with Carson, and the "Stump the Band" routine in which a request for an obscure song was met by a cry of "key of E" and an invented country number. Tommy Newsom conducted when he was away. The band that moved to Burbank carried New York veterans and a West Coast jazz bench that included Conte Candoli, Snooky Young, Bill Perkins, Pete Christlieb, Ernie Watts and Ed Shaughnessy, and in the New York years the trumpet section had included Clark Terry.

His own records began on the Command label in the early 1960s, first as big-band swing and by the end of the decade as the studio instrumental pop of the "now sound," often with arrangements by Dick Hyman. He moved to RCA Victor in 1971 and made Brass on Ivory (1972) and Brass, Ivory & Strings (1973) with Henry Mancini. Night Journey (Epic, 1976), recorded in Dallas with arrangements by Fred Crane, was a jazz-funk record that produced the dance-club hits "Night Journey" and "I Wanna Be with You"; his recording of "Melody (Aria)" reached the Adult Contemporary Top 40 in early 1977. In 1985 he recorded with the fusion group Xebron for Passport. Then, in August 1986, he finally took the Tonight Show Band into the studio: The Tonight Show Band with Doc Severinsen (Amherst, 1986) was recorded live in the studio over three days in Hollywood, and it won the Grammy Award for Best Jazz Instrumental Performance, Big Band at the 29th Annual Grammy Awards on February 24, 1987 (the category is now called Best Large Jazz Ensemble Album). A second volume followed, and Facets (Amherst, 1988), which paired him with fusion groups and string orchestras, was a Top Ten jazz album.

After the show ended he moved to Mexico and formed the San Miguel Five, and toured with Tonight Show alumni including Conte Candoli, Snooky Young, Bill Perkins, Ernie Watts, Ross Tompkins and Ed Shaughnessy. In parallel he built a second career on the orchestra circuit. He became principal pops conductor of the Phoenix Symphony in 1983, then held the same post with the Buffalo Philharmonic, the Milwaukee Symphony and the Minnesota Orchestra, and he recorded trumpet showcases for Telarc with Erich Kunzel and the Cincinnati Pops. He retired from conducting in 2007 and is Pops Conductor Emeritus in Milwaukee and Pops Conductor Laureate in Minnesota. He was visiting professor of music at Arizona State University in 2001 and 2002 and was inducted into the Scandinavian-American Hall of Fame in 2014. Among his later recordings are the San Miguel Five's Oblivion (2013) and Prime Time (2014), a big-band album with the Alan Baylock Jazz Orchestra on which he is the special guest. The documentary Never Too Late: The Doc Severinsen Story premiered on PBS American Masters on April 2, 2021. He played what was billed as his final concert on September 1, 2022, with the San Miguel Five in Saratoga Springs, New York, at the age of 95, and he turned 99 in July 2026.

Severinsen is a case where the public career and the jazz career point in different directions, and both are documented. Most listeners know him as the bandleader on late-night television and as the maker of pop, disco and orchestral-pops records, and his own albums were mostly not jazz. AllMusic notes that jazz critics held that against him, and that he did not often show his chops. The same entry calls him an able bebop soloist with a bright, clean tone and a tremendous range in the upper register of the horn, and the credit list bears that out: trumpet chairs in the big bands of Gerry Mulligan, Dizzy Gillespie, Stan Getz and Milt Jackson, a Grammy in the big-band jazz category, and a Tonight Show band whose players included many West Coast jazz soloists. His first model was Harry James, and his sound, big, bright and secure at the top of the range, belongs to the swing-era lead-trumpet tradition, extended into the session world of Command Records and the New York studios of the early 1960s. Crossover Jazz is the honest label for a career that moved between studio jazz, television, instrumental pop, fusion and symphonic pops.