The comedians led separate careers in the vaudeville tradition, but it was when they teamed up that they gained popularity. Gallagher and Shean first joined forces during the tour of "The Rose Maid" in 1912, but they quarreled and split up two years later. They next appeared together in 1920, through the efforts of Shean's sister, Minnie Marx.-- the mother of the Marx Brothers, This pairing lasted until 1925 and led to their fame.Gallagher and Shean remain best known for their theme song , which was a hit in the 1922 Ziegfeld Follies. Bryan Foy, son of stage star Eddie Foy and eldest member of the "Seven Little Foys", claimed to have written the song, but it is officially attributed to Gallagher and Shean. The song endured in popularity and was regularly tweaked and updated with additional verses, so several different versions of the song are still extant. The song was recorded as two-sides of a 10" 78 in 1922 for Cameo. Naxos attributes to song to Irving and Jack Kaufman. The recording was extremely popular and well-remembered: a parody of it was recorded by Bing Crosy and Johnny Mercer in the late 1930s, another parody was performed by Jackie Gleason and Groucho Marx (who was Al Shean's nephew) on television in the late 1950s, and Lenny Bruce was able to make an offhanded reference to it in his nightclub act of the 1960s, all of them confident that audiences would recognize it right away.With occasional exceptions, each verse of the song ended with Gallagher speaking a punchline, followed by Shean singing "Absolutely, Mister Gallagher?" and Shean replying "Positively, Mister Shean!". This cross-talk format continues to be imitated, parodied and referenced for audiences who may have no knowledge of the original. Cartoonist Bobby London depicted his characters Dirty Duck and Weevil telling each other "Posilutely, Weevil!" "Absotively, Mr. Duck!". In the 1990s, a radio commercial for Pitney Bowes office equipment used the original tune with new lyrics: "Absolutely, Mister Pitney!" "Positively, Mister Bowes!"
Capitalizing on the post-King Tut craze for everything Egyptian, Gallagher and Shean appeared in Egyptian dress (Gallagher in the pith helmet and white suit of the tourist, Shean in the fez and oddly skirted jacket of a "native" Egyptian colonial).
In 1921, they were sued by the Shubert organization for breach of contract. According to Shubert, they could not perform for the competing Ziegfeld Follies. The case claimed that Gallagher and Shean's act was "unique and irreplaceable." The comedians' defense was that their act was mediocre and the judge initially found in their favor, although the decision was later reversed.
For a time in the 1920s, Gallagher was involved with his protegee, vivacious French-Canadian dancer Fifi D'Orsay.
Gallagher and Shean often had personal differences during their partnership (the constant backstage hostilities inspired Neil Simon to incorporate them into his successful show-business-themed comedy The Sunshine Boys).Ed Gallagher died in 1929; Al Shean worked occasionally thereafter as a solo character actor. The 1941 Metro-Goldwyn-Mayer musical Ziegfeld Girl features a re-creation of Gallagher and Shean's act, with Al Shean in his familiar role and costume, and character actor Charles Winninger portraying Gallagher.