Newly discharged, Mancini entered the music industry. Entering 1946, he became a pianist and arranger for the newly re-formed Glenn Miller Orchestra, led by 'Everyman' Tex Beneke. After World War II, Mancini broadened his skills in composition, counterpoint, harmony and orchestration during studies opening with the composers Ernst Krenek and Mario Castelnuovo-Tedesco.
In 1952, Mancini joined the Universal Pictures music department. During the next six years, he contributed music to over 100 movies, most notably Creature from the Black Lagoon, The Creature Walks Among Us, It Came from Outer Space, Tarantula, This Island Earth, The Glenn Miller Story (for which he received his first Academy Award nomination), The Benny Goodman Story, and Orson Welles's Touch of Evil. During this time, he also wrote some popular songs. His first hit was a single by Guy Lombardo and His Royal Canadians titled "I Won't Let You Out of My Heart."
Mancini left Universal-International to work as an independent composer/arranger in 1958. Soon afterward, he scored the television series Peter Gunn for writer/producer Blake Edwards. This was the genesis of a relationship in which Edwards and Mancini collaborated on 30 films over 35 years. Along with Alex North, Elmer Bernstein, Leith Stevens and Johnny Mandel, Henry Mancini was a pioneer of the inclusion of jazz elements in the late romantic orchestral film and TV scoring prevalent at the time.
Mancini's scores for Blake Edwards included Breakfast at Tiffany's (with the standard "Moon River") and Days of Wine and Roses (with the title song), as well as Experiment in Terror, The Pink Panther (and all of its sequels), The Great Race, The Party, 10 (including "It's Easy to Say"), and Victor Victoria. Another director with whom Mancini had a longstanding partnership was Stanley Donen (Charade, Arabesque, Two for the Road). Mancini also composed for Howard Hawks (Man's Favorite Sport?, Hatari! – which included the well-known "Baby Elephant Walk"), George Roy Hill (The Great Waldo Pepper), Arthur Hiller (Silver Streak), and others.
Mancini scored many TV movies, including The Moneychangers, The Thorn Birds, and The Shadow Box. He wrote many television themes, including Mr. Lucky (starring John Vivyan and Ross Martin), NBC Mystery Movie, What's Happening!!, and Once Is Not Enough.
Mancini recorded over 90 albums, in styles ranging from big band to light classical to pop. Eight of these albums were certified gold by the Recording Industry Association of America.
Mancini's album discography includes:
- Academy Award Songs, Vol. 2 (RCA Victor PRS-175; created as a premium for B.F. Goodrich)
- Arabesque (1966, RCA Victor LPM-3623 (mono), LSP-3623 (stereo))
- The Big Latin Band of Henry Mancini (1968, RCA Victor LSP-4049)
- The Blues and the Beat (1960, RCA Victor LPM-2147 (mono), LSP-2147 (stereo))
- Breakfast at Tiffany’s (1961, RCA Victor LPM-2362 (mono), LSP-2362 (stereo)) Music from the film.
- Charade (1963, RCA Victor LPM-2755 (mono), LSP-2755 (stereo)) Music from the film.
- Combo! (1961, RCA Victor LPM-2258 (mono), LSP-2258 (stereo))
- The Concert Sound of Henry Mancini (1964, RCA Victor LPM-2897 (mono), LSP-2897 (stereo))
- Days of Wine and Roses & Others (1973, RCA Camden ACL 7035; re-released on Pickwick ACL-7035)
- Dear Heart and Other Songs About Love (1965, RCA Victor LPM-2990 (mono), LSP-2990 (stereo))
- Debut! (1969, RCA Red Seal LSC-3106; with The Philadelphia Orchestra Pops)
- Dream Of You (1971, RCA Camden CAS-2510)
- Driftwood and Dreams (Liberty LRP-3049; re-release of The Versatile Henry Mancini and His Orchestra)
- Encore! More of the Concert Sound of Henry Mancini (1967, RCA Victor LPM-3887 (mono), LSP-3887 (stereo))
- Experiment in Terror (1962, RCA Victor LPM-2442 (mono), LSP-2442 (stereo))
- Gaily, Gaily (1969, United Artists UAS-5202) Music from the film.
- The Great Race (1965, RCA Victor LPM-3402 (mono), LSP-3402 (stereo)) Music from the film.
- Gunn… Number One! (1967, RCA Victor LPM-3840 (mono), LSP-3840 (stereo)) Music from the film Gunn.
- Hangin’ Out (1974, RCA Victor CPL-1-0672)
- Hatari! (1962, RCA Victor LPM-2559 (mono), LSP-2559 (stereo)) Music from the film.
- The Hawaiians (1970, United Artists UAS-5210) Music from the film.
- Henry Mancini Presents the Academy Award Songs (1966, RCA Victor LPM-6013 (mono), LSP-6013 (stereo))
- Henry Mancini Favorites (1964, Crown CLP 5459 (mono), CST 459 (stereo))
- His Sound is His Signature (1969, RCA SPS-33-557)
- The Latin Sound of Henry Mancini (1965, RCA Victor LPM-3356 (mono), LSP-3356 (stereo))
- Mancini ’67 (1967, RCA Victor LSP-3694)
- Mancini Concert (1971, RCA Victor LSP-4542)
- Mancini Plays Mancini and Other Composers (1967, RCA Camden CAL-2158 (mono), CAS-2158 (stereo))
- Mancini Plays the Great Academy Award Songs (1964, RCA Victor PRM-151 (mono), PRS-151 (stereo))
- Mancini Plays the Theme from Love Story (1970, RCA Victor LSP-4466)
- The Mancini Sound (1968, RCA Victor LPM-3943 (mono), LSP-3943 (stereo))
- The Mancini Touch (1960, RCA Victor LPM-2101 (mono), LSP-2101 (stereo))
- Me, Natalie (1969, Columbia OS 3350; with Rod McKuen) Music from the film.
- The Molly Maguires (1970, Paramount PAS-6000) Music from the film.
- More Music from Peter Gunn (1959, RCA Victor LPM-2040 (mono), LSP-2040 (stereo)) Music from the TV series.
- Mr. Lucky Goes Latin (1961, RCA Victor LPM-2360 (mono), LSP-2360 (stereo))
- Music from Mr. Lucky (1960, RCA Victor LPM-2198 (mono), LSP-2198 (stereo)) Music from the TV series.
- The Music from Peter Gunn (1959, RCA Victor LPM-1956 (mono), LSP-1956 (stereo)) Music from the TV series. An absolute classic of the Crime Jazz genre.
- Music from the Motion Picture Score ‘High Time’ (1960, RCA Victor LPM-2314 (mono), LSP-2314 (stereo) Music from the film.
- Music of Hawaii (1966, RCA Victor LPM-3713 (mono), LSP-3713 (stereo))
- Our Man in Hollywood (1963, RCA Victor LPM-2604 (mono), LSP-2604 (stereo))
- The Party (1968, RCA Victor LPM-3997 (mono), LSP-3997 (stereo)) Music from the film.
- The Pink Panther (1963, RCA Victor LPM-2795 (mono), LSP-2795 (stereo)) Music from the film.
- The Second Time Around and Others (1966, RCA Camden CAL-928 (mono), CAS-928 (stereo))
- Six Hours Past Sunset (1969, RCA Victor LSP-4239)
- The Sounds & Voices of Henry Mancini (1966, Sunset SUM-1105 (mono), SUS-5105 (stereo))
- Sunflower (1970, Avco Embassy AVE-0-11001) Music from the film.
- Symphonic Soul (1975, RCA Victor APL1-1025)
- Theme From “Z” and Other Film Music (1970, RCA Victor LSP-4350)
- Touch of Evil (1958, Challenge LP-602) Music from the film.
- Two for the Road (1967, RCA Victor LPM-3802 (mono), LSP-3802 (stereo)) Music from the film.
- Uniquely Mancini (1963, RCA Victor LPM-2692 (mono), LSP-2692 (stereo))
- The Versatile Henry Mancini and His Orchestra (1959, Liberty LRP-3121 (mono), LST-7121 (stereo); re-released as Driftwood and Dreams)
- A Warm Shade of Ivory (1969, RCA Victor LSP-4140)
- What Did You Do in the War, Daddy? (1966, RCA Victor LPM-3648 (mono), LSP-3648 (stereo)) Music from the film.
- The Wild Side of Henry Mancini (1962, Challenge CH 615)