Jenkins was born Alfred McGonegal on Staten Island, New York on April 9, 1900.
He studied at the American Academy of Dramatic Arts. In his first stage appearance, he danced next to James Cagney in a chorus line for an off-Broadway musical called Pitter-Patter, earning five dollars a week. He also appeared in Broadway plays between 1923 and 1962, including The Front Page (1928). His big break came when he replaced Spencer Tracy for three weeks in the Broadway play The Last Mile.
Jenkins was called to Hollywood by Darryl F. Zanuck and signed first to Paramount Pictures and shortly afterward to Warner Bros. His first role in films came in 1931, when he appeared as an ex-convict in the short Straight and Narrow. He had originated the character of Frankie Wells in the Broadway production of Blessed Event and reprised the role in its film adaptation, both in 1932. With the advent of talking pictures, he made a career out of playing comic henchmen, stooges, policemen, taxi drivers, and other 'tough guys' in numerous films of the 1930s and 1940s, especially for Warner Bros. Allen Jenkins was labeled the "greatest scene-stealer of the 1930s" by The New York Times. In 1959, Jenkins played the role of elevator operator Harry in the comedy Pillow Talk.
Jenkins later voiced the character of Officer Charlie Dibble on the Hanna-Barbera TV cartoon, Top Cat (1961–62). He was a regular on the television sitcom Hey, Jeannie! (1956–57), starring Jeannie Carson and often portrayed Muggsy on the 1950s-1970s CBS series The Red Skelton Show. He was also a guest star on many other television programs, such as The Man from U.N.C.L.E., Mr. & Mrs. North, I Love Lucy, Playhouse 90, The Ernie Kovacs Show, Zane Grey Theater, and Your Show of Shows. He had a cameo appearance in It's a Mad, Mad, Mad, Mad World (1963). Eleven days before his death, he made his final appearance, at the end of Billy Wilder's remake of The Front Page (1974); it was released posthumously.
Jenkins died of lung cancer early on July 20, 1974. He was 74 years old.
