Martin Louis Paich was born on January 23, 1925, in Oakland, California. He learned accordion and piano as a child and was leading bands and playing weddings by the age of ten; by sixteen he was working professionally and writing arrangements for the local bandleader Gary Nottingham alongside Pete Rugolo. He was drafted in 1943 and led an Army Air Corps band until 1946. After the war he studied composition and arranging in Los Angeles, with teachers that included Mario Castelnuovo-Tedesco and Arnold Schoenberg, and he earned a master's degree in composition from the Los Angeles Conservatory of Music in 1951.

In the early 1950s he found work as a pianist and arranger with the bands of Jerry Gray and Dan Terry, then moved into the Los Angeles jazz scene around Shelly Manne and Shorty Rogers, playing and writing for both in 1953 and 1954 and appearing on the 1954 Decca LP Jazz Studio 2 from Hollywood. He also served a stretch as accompanist and music director for Peggy Lee. In 1955 he began recording under his own name for a run of small labels, among them Mode, Tampa and Bethlehem, and he arranged and played on the soundtrack of the Disney film Lady and the Tramp (1955). His first jazz records as a leader included the Bethlehem LP Jazz Music for the Birds and the Hep Cats, shared with the arranger Russ Garcia, and Tenors West, a session for Gene Norman's label recorded in November 1955 in which his octet backed four tenor saxophonists: Jimmy Giuffre, Bob Cooper, Harry Klee and Bob Enevoldsen. In August 1956 he cut the Tampa sessions The Marty Paich Quartet Featuring Art Pepper and Hot Piano, and in June 1957 he recorded the big-band album that Cadence issued as The Picasso of Big Band Jazz.

The partnership that made his name began when the singer Mel Tormé moved from Decca to Bethlehem in 1955 and asked to work with him. The ten-piece group that Tormé proposed, the Dek-tette, was modeled on the tentette of Gerry Mulligan and used a brass quintet of two trumpets, trombone, French horn and tuba with alto, tenor and baritone saxophones over bass and drums, and, at Tormé's urging, no piano. The first album, Mel Tormé with the Marty Paich Dek-tette (1956), opened with "Lulu's Back in Town" and featured Pete Candoli and Don Fagerquist on trumpets, Bud Shank on alto, Bob Cooper on tenor, Red Mitchell on bass and Mel Lewis on drums. Paich kept the band together for Mel Tormé Sings Fred Astaire, recorded in November 1956, and a remake of Tormé's extended work California Suite (March 1957), and he wrote for the same group behind other singers, including Jeri Southern, the Hi-Lo's and Ella Fitzgerald on Ella Swings Lightly (1958). Tormé and Paich came back together at Verve for Mel Tormé Swings Shubert Alley (1960), with Art Pepper, Bill Perkins, Frank Rosolino and Stu Williamson in the band.

Through the second half of the 1950s Paich wrote for much of the West Coast jazz community, including Dave Pell's octet, Chet Baker, Buddy Rich, Stan Kenton, Anita O'Day and Ray Brown, whose Bass Hit! he arranged and conducted. For Pepper he scored Art Pepper + Eleven: Modern Jazz Classics, recorded on March 14, March 28 and May 12, 1959, and released by Contemporary in 1960, giving the altoist a band built from Los Angeles first-call players on arrangements of bebop pieces such as "Move," "Groovin' High" and "Donna Lee." His own Warner Bros. LPs The Broadway Bit and I Get a Boot Out of You (both 1959) drew on the same pool of Los Angeles soloists, with Pepper, Jimmy Giuffre and the young bassist Scott LaFaro on the first. Two albums for RCA Victor with his Jazz Piano Quartet, Take Me Along (recorded in 1959) and Lush, Latin & Cool (recorded in June 1960), were the last of his main run as a leader; the second put four pianists on the bandstand, Paich, Jimmy Rowles, Pete Jolly and John Williams.

From around 1960 he put his recording career aside to arrange for pop and jazz singers. He wrote the string arrangements for Ray Charles's Modern Sounds in Country and Western Music (1962), arranged and conducted Lena Horne's Lena...Lovely and Alive (1962), and arranged albums for Al Hirt, Hank Crawford, Helen Humes, Sammy Davis Jr., Jack Jones, Dean Martin, Andy Williams and Barbra Streisand, returning to Fitzgerald for Whisper Not (1966). He wrote one more album under his own name in the decade, the Reprise LP The Rock-Jazz Incident (1966), and scored films including Hey There, It's Yogi Bear! (1964), The Man Called Flintstone (1966), The Swinger (1966) and Changes (1969). On television he led studio orchestras for The Glen Campbell Goodtime Hour and The Sonny & Cher Comedy Hour, took over from Nelson Riddle on The Smothers Brothers Comedy Hour, and won an Emmy in 1974 for his music for the drama series Ironside.

His output slowed after the early 1970s, but he kept working as a conductor and string arranger for George Benson, Carly Simon, Elton John, Kenny Loggins, whose "Only a Miracle" brought him a Grammy-nominated arrangement, and Toto, the band co-founded by his son, the keyboardist David Paich. With his son he arranged and produced Sarah Vaughan's Songs of the Beatles (1981), and he kept working on film scores as orchestrator and conductor into the 1990s. In 1988 he rebuilt the Dek-tette for Reunion, recorded for Concord Jazz with Tormé, and the group's last release, In Concert Tokyo, documented the band's appearance at the Fujitsu-Concord Jazz Festival in Tokyo. Paich passed away from colon cancer on August 12, 1995, at his home in Santa Ynez, California, at the age of 70.

AllMusic's Steve Huey singled out Paich's ability to make small ensembles sound as full as large orchestras, and the Dek-tette is the clearest case: ten players voiced with tuba pedal points, shout choruses that let the singer ride the horn lines like an eleventh member of the band, block scoring and a habit of quoting other songs inside an arrangement. Thomas Cunniffe, writing on the Tormé collaboration, noted that Paich enjoyed working out ideas with a singer rather than simply handing over charts, and that each Dek-tette LP was built around a single stylistic idea. His teachers included Castelnuovo-Tedesco and Schoenberg, his sound came out of the cool-school West Coast writing of Shorty Rogers and Pete Rugolo and the Mulligan tentette, and he was one of the arrangers other Los Angeles bandleaders and singers called when they wanted a jazz setting with studio polish. Huey wrote that his jazz credentials were much stronger than those of many of his peers among postwar arrangers. After 1960 most of his visible work was for pop singers, television and film, so the jazz record rests on a compact body of work from roughly 1955 to 1961 and the two Tormé reunion albums, and Mel Tormé Swings Shubert Alley made the Penguin Guide to Jazz Recordings' suggested core collection.