Born in Koblenz, Rhineland-Palatinate, Germany. In the US from age four, he was raised and educated in Chicago and began his career writing special material for vaudeville acts. From the mid-20s he contributed songs to Broadway and Hollywood musicals, in collaboration with such composers as Walter Donaldson, George Gershwin, Sigmund Romberg, Victor Schertzinger, and Bronislaw Kaper. His best-known songs include "Pretty Baby," "Some Sunday Morning," "Ain't We Got Fun?," "My Buddy," "Carolina in the Morning," "Side by Side," "Toot Toot Tootsie Goodbye," "Nobody's Sweetheart," "I'll See You in My Dreams," "Charley My Boy," "It Had to Be You," "Yes Sir, That's My Baby," "Love Me or Leave Me," "Makin' Whoopee," "Beloved," "Coquette," "Flying Down to Rio," "The Carioca," "Orchids in the Moonlight," and "San Francisco." Kahn's story was told in the biographic film I'LL SEE YOU IN MY DREAMS (1951), in which he was portrayed by Danny Thomas. Doris Day played his wife and sometime collaborator Grace LeBoy Kahn.

Nominated for Music Scoring Awards (Best Score) 1934: ONE NIGHT OF LOVE (w. Victor Schertzinger and Louis Silvers, as head of department)    Nominated for Music (Best Song) 1934: FLYING DOWN TO RIO "The Carioca"- Lyric (w. Edward Eliscu)    Nominated for Music (Best Song) 1940: SPRING PARADE "Waltzing in the Clouds"- Lyric 3 nominations