Chaplin first toured America with the Fred Karno troupe from 1910 to 1912. Then, after five months back in England, he returned for a second tour and arrived in the United States with the Karno Troupe on October 2, 1912. In the Karno Company was Arthur Stanley Jefferson, who would later become known as Stan Laurel. Chaplin and Laurel shared a room in a boarding house. Stan Laurel returned to England but Chaplin remained in the United States. In late 1913, Chaplin's act with the Karno Troupe was seen by film producer Mack Sennett, who hired him for his studio, the Keystone Film Company. Chaplin's first film appearance was in Making a Living a one-reel comedy released on February 2, 1914. At Keystone Studios, Chaplin became an instant success[4]. Chaplin once entered a Charlie Chaplin look-a-like contest in San Francisco and, quite humorously, could not make it to the final round[5].

Pioneering film artist
Kid Auto Races in Venice (1914): Chaplin's second film and the début of his "tramp" costume.
Kid Auto Races in Venice (1914): Chaplin's second film and the début of his "tramp" costume.

Chaplin's earliest films were made for Mack Sennett's Keystone Studios, where he developed his tramp character and very quickly learned the art and craft of film making. The tramp was first presented to the public in Chaplin's second film Kid Auto Races at Venice (released Feb. 7, 1914) though Mabel's Strange Predicament, his third film, (released Feb. 9,1914) was produced a few days before. It was for this film that Chaplin first conceived of the tramp. The character would immediately gain huge popularity among theater audiences[4]. As Chaplin recalled in his autobiography:

"I had no idea what makeup to put on. I did not like my get-up as the press reporter [in Making a Living]. However on the way to the wardrobe I thought I would dress in baggy pants, big shoes, a cane and a derby hat. I wanted everything to be a contradiction: the pants baggy, the coat tight, the hat small and the shoes large. I was undecided whether to look old or young, but remembering Sennett had expected me to be a much older man, I added a small moustache, which I reasoned, would add age without hiding my expression.
I had no idea of the character. But the moment I was dressed, the clothes and the makeup made me feel the person he was. I began to know him, and by the time I walked on stage he was fully born." (Chaplin, My Autobiography: 154).

Chaplin's early Keystones use the standard Mack Sennett formula of extreme physical comedy and exaggerated gestures. Chaplin's pantomime was subtler, more suitable to romantic and domestic farces than to the usual Keystone chases and mob scenes. The visual gags were pure Keystone, however; the tramp character would aggressively assault his enemies with kicks and bricks. Moviegoers loved this cheerfully earthy new comedian, even though critics warned that his antics bordered on vulgarity. Chaplin was soon entrusted with directing and editing his own films. He made 34 shorts for Sennett during his first year in pictures, as well as the landmark comedy feature Tillie's Punctured Romance.

In 1915, Chaplin signed a much more favourable contract with Essanay Studios, and further developed his cinematic skills, adding new levels of depth and pathos to the Keystone-style slapstick. Most of the Essanay films were more ambitious, running twice as long as the average Keystone comedy. Chaplin also developed his own stock company, including ingenue Edna Purviance and comic villains Leo White and Bud Jamison.

In 1916, the Mutual Film Corporation paid Chaplin US$670,000 to produce a dozen two-reel comedies. He was given near complete artistic control, and produced twelve films over an eighteen-month period that rank among the most influential comedy films in cinema. Practically every Mutual comedy is a classic: Easy Street, One AM, The Pawnshop, and The Adventurer are perhaps the best known. Edna Purviance remained the leading lady, and Chaplin added Eric Campbell, Henry Bergman, and Albert Austin to his stock company; Campbell, a Gilbert and Sullivan veteran, provided superb villainy, and second bananas Bergman and Austin would remain with Chaplin for decades. Chaplin regarded the Mutual period as the happiest of his career, although he also had concerns that the films during that time were becoming formulaic owing to the stringent production schedule his contract required. Upon the US entering World War I, Chaplin became a spokesman for Liberty Bonds with his close friend Douglas Fairbanks and Mary Pickford[4].

Most of the Chaplin films in circulation date from his Keystone, Essanay, and Mutual periods. After Chaplin assumed control of his productions in 1918 (and kept exhibitors and audiences waiting for them), entrepreneurs serviced the demand for Chaplin by bringing back his older comedies. The films were recut, retitled, and reissued again and again, first for theatres, then for the home-movie market, and in recent years, for home video. Even Essanay was guilty of this practice, fashioning "new" Chaplin comedies from old film clips and out-takes. The twelve Mutual comedies were revamped as sound movies in 1933, when producer Amadee J. Van Beuren added new orchestral scores and sound effects. A listing of the dozens of Chaplin films and alternate versions can be found in the Ted Okuda-David Maska book Charlie Chaplin at Keystone and Essanay: Dawn of the Tramp. Efforts to produce definitive versions of Chaplin's pre-1918 short films have been underway in recent years; all twelve Mutual films were restored in 1975 by archivist David Shepard and Blackhawk Films, and new restorations with even more footage were released on DVD in 2006.