Hallett studied at the Boston Conservatory of Music. During the first world war , he played in France as a member of the Orchestra of Al Moore to the Allied soldiersentertained. Then he had his own group, with which he also took up. Around 1930 he broke his arm in five places, got pneumonia and his doctors advised him to take rest for long periods. After his comeback, he played no instruments more, but was limited to leading a band. In the following years he had his own band, applied by especially in New England played and had a lot of success. He also appeared in the famous Roseland Ballroom in New York.
In his and vocalists who later became known to a greater or lesser extent, such as Gene Krupa, Jack Teagarden, Frankie Carle, Jack Jenney, Toots Mondello, Irene Daye, Clark Yocum, Floyd O'Brien, Spud Murphy, Boots Mussulli, Brad Gowans, Turk Murphy, Teddy Grace and Don Fagerquist. Its theme song was "Boston Tea Party".
Mallett has recorded in the second half of the 1930s, especially for Vocalion and Decca Records, big hits, but has never had. His career later had to suffer from the fact that he as older band leader at one point no young fans could win more for his music. He also had alcohol problems. He was active as a bandleader until in the 1950s.
Mal Hallett died from a heart attack.