Vallee played clarinet and saxophone in various bands around New England in his youth, in the mid 1920s played with the Savoy Havana Band in London. He then returned to the States to form his own band, Rudy Vallee and the Connecticut Yankees. With this band he started taking vocals (supposedly reluctantly at first). He had a rather thin tenor voice and seemed more at home singing sweet ballads than attempting vocals on jazz numbers. However his singing, together with his suave manner and handsome good looks attracted great attention, especially from young women. Vallee was given a recording contract, and in 1928 started performing on the radio.
Vallee became the most prominent of a new style of popular singer, the "crooner". Previously popular singers neaded strong projecting voices to fill theaters in the days before the electric microphone. Crooners had soft voices that were well suited to the intimacy of the new medium of radio.
Vallee became also perhaps the first complete example of the 20th century mass media pop-star. Flappers mobbed him wherever he went. His live appearances were usually sold out, and even if his singing could hardly be heard in those venues not yet equipt with the new electronic microphones, his screaming female fans went home happy if they had caught sight of his lips through the opening of the trademark megaphone he sang through.
In 1929 Vallee did his first film "Vagabond Lover". His first films were made to cash in on his singing popularity, but Hollywood was pleasantly surprised to find that Vallee could act as well. Also in 1929 Vallee started hosting The Fleishchman’s Yeast Musical Variety Hour; he would continue hosting popular radio variety shows through the 1940s. When Vallee took his contractual vactions from his national radio show in 1936, he insisted his sponsor hire Louis Armstrong as his substitute. That same year Vallee also wrote the introduction for Armstrong's book "Swing That Music".
In middle age Vallee's voice matured into a robust baritone. (In his later years he told a collector of his early records that "Everything I did before 1950 you can shit on.") He performed on Broadway in the show "How To Succeed in Business Without Really Trying" and appeared in the film of the same name. He appeared in the 1960s Batman television show as the character "Lord Marmaduke Fogg". He toured with a one-man theater show into the 1980s.