In 1901, he was discovered and promoted by David Belasco who starred him in The Auctioneer, in which he played 1,400 times, including a revival that extended over several seasons.

Although he appeared in many productions, his fortune and success in theater centered on his playing four major roles over a 25-year period: Simon Levi in The Auctioneer (1901), Anton von Barwig in The Music Master (1904), Wes Bigelow in A Grand Army Man (1907) and the title role in The Return of Peter Grimm (1911).

[3] One of his best-known roles was that of Anton von Barwig in The Music Master, which he played from 1904 to 1908, appearing in the part more than 1000 times.

[3] In 1911 Warfield created the title role in The Return of Peter Grimm, a play Cecil B. DeMille claimed that David Belasco stole from him.

Warfield's position as a leading American actor in comedy was established by the masterly style in which he portrayed, in each of these plays, a kindly old gentleman who is pathetic in misfortune and amusingly eccentric.