Garrett was never a "looker", but she could sing and dance with the best of them. She made her stage debut in 1938 with the Mercury Theatre in "Danton's Death", and also danced with Martha Graham and performed at the 1939 World's Fair. She played on Broadway in "All in Fun" (1941), "Let Freedom Sing" (1942), "Call Me Mister" (1946) and others musicals before an MGM contract lured her to Hollywood. Garrett's first film was the non-musical "The Big City" (1948), in which three men see who can marry first so they can adopt Margaret O'Brien. She played the prospective bride of George Murphy. From there, she was put into "Words and Music" (1948), the sanitized biography of Rodgers and Hart in which she sang "Manhattan" with Mickey Rooney, and "On the Town" (1949), as the female taxi driver romanced by Frank Sinatra, but Garrett's greatest musical success was in "My Sister Eileen" for Columbia (1955), in which she played the plain-Jane sister often overshadowed by the tempting Eileen (Janet Leigh). But, her husband, Larry Parks, had been the first actor called before the House Committee on un-American Activities as an unfriendly witness, and although he named names, Parks' career tumbled. In deference to him and the unpleasant aura in Hollywood, Garrett stopped acting in films after "Shadow on the Window" (1957). Although she made her TV debut in an episode of "Ford Theatre" (1955), with the exception of an appearance on "The Art Carney Show" (1959) and two TV specials in 1960, she was hardly seen on that medium as well. Instead, Garrett and Parks tended to raising two sons--one of whom would become actor Andrew Parks--and running a real estate business. They also performed on stage, which was still occasionally open to Parks, including a concert of songs at the London Palladium in 1950. Garrett also returned to Broadway in "Bells Are Ringing" (1958), replacing Judy Holliday in the role of the answering service attendant. Garrett also appeared on Broadway in "Beg, Borrow or Steal" (1960) and "A Girl Could Get Lucky" (1964).

Garrett was little seen by the general public until 1973, when Norman Lear added her to the cast of "All in the Family". As the feminist Irene Lorenzo, she frequently sparred with Carroll O'Connor's Archie Bunker. She also performed a one-woman show in Los Angeles called "Betty Garrett and Other Songs". When Parks died in 1975, Garrett left the cast of "All in the Family". The following year, she joined the cast of "Laverne & Shirley" as the title characters' landlady and eventually married Laverne's father (Phil Foster). She remained with the series until its demise in 1981. Having earned the nest egg the blacklisting had denied herself and Parks through her TV work, Garrett was less active in the 80s and 90s. She returned to Broadway again in "The Supporting Cast" (1981), and played a key role in "Quilters" at the Mark Taper Forum in Los Angeles (1984), but other work became infrequent. She was interviewed occasionally on retrospective programs about the Hollywood musical heyday and studio system, and in 1995 appeared on the American Movie Classics channel about the studios in a roundtable chat program with George Sidney, the director of many MGM musicals, and June Lockhart.