Born in Donaldsonville, Louisiana, he and his pianist brother Ray first recorded as the Johnson Brothers in New Orleans in the late 1940s, and Plas then toured with R&B singer Charles Brown. After army service, he moved to Los Angeles and began session recordings as a full-time musician, backing artists such as B.B. King and Johnny Otis as well as scores of other R&B performers. An early supporter was Maxwell Davis, who hired him to take over his own parts so that he could concentrate on producing sessions for the Modern record label.
Recruited by Capitol Records in the mid-1950s, Johnson also played on innumerable records by Peggy Lee, Nat "King" Cole, Glen Gray, Frank Sinatra and others. He remained a leading session player for almost twenty years, averaging two sessions a day and playing everything from movie soundtracks to rock and roll singles, by such artists as Ricky Nelson and Bobby Vee. He played on many of the Beach Boys’ records, and was an integral part of a number of instrumental groups that existed in name only, such as B. Bumble and the Stingers and The Pets. In the late 1950s and early 1960s he was a regular member of Henry Mancini's studio orchestra and in 1963 he recorded the Pink Panther theme. Another solo for a well-known television series was on The Odd Couple's theme music. Johnson was also used by Motown, and played on hits by Marvin Gaye, the Supremes and others. Johnson also played on sessions for Nancy Sinatra.
Johnson can be heard on the 1963 album "Ella Fitzgerald Sings the Jerome Kern Songbook", recorded with the esteemed arranger Nelson Riddle. His sax is also heard on two of the other greatElla Fitzgerald songbooks - The Harold Arlen Songbook and The Johnny Mercer Songbook.
In 1964, Johnson was the featured performer on "Blue Martini" ( Ava Records ), a concept album by John Neel. It was a groundbreaking album, with the saxophone being the lead "voice" surrounded by a full string section. This jazz/classical hybrid contains some of Johnson's best and most innovative playing, with the standout being "Bury Me Blue".
In 1970, he joined the studio band for "The Merv Griffin Show" and also played with a number of jazz and swing bands of the period. He continues to record and perform, particularly at jazz festivals.
Johnson currently performs on T990 (brass) and T9937 (solid silver) tenor saxophones made by Yanagisawa. He uses a very open (140/2) Berg Larsen stainless steel mouthpiece with Rico Plasticover no. 2 reeds, a setup that enables him to produce his very distinctive and instantly recognizable sound.