Pat Sullivan was born in Australia, as the son of a Darlinghurst cab proprietor. After leaving school, he worked at various jobs, including as gatekeeper at Toohey's brewery in Surry Hills. He attended classes at the Art Society of NSW, while doing his first assignments as a caricaturist. Between 1905 and 1907, he submitted humorous cartoons to the trade union newspaper, The Worker. In 1909, Sullivan emigrated to England, where he tried his hand on lightweigh boxing as well as singing and dancing in music halls. His first actual comics work was contributing to the 'Ally Sloper' strip for a year and a half.
Sullivan emigrated to the United States in 1914, where he initially earned his living designing cinema posters. But in that same year, the McClure newspaper syndicate assigned him to do the comic strip 'The Adventures of Sambo'. Other strips by Sullivan include 'Johnny Boston Beans', 'Obliging Oliver' and 'Old Pop Perkins'.
In 1915 Sullivan started a career in animation, eventually owning his own studio, where his first recorded effort seemed to be an animated version of 'Pa Perkins'. In 1917, he created an animation called 'The Tail of Thomas Kat', featuring the prototype of the later Felix. From 1919, more than a hundred 'Felix the Cat' cartoons were published, and the animated Felix appeared all over the world by the time of Sullivan's death in 1933.
After Sullivan's death, co-worker Otto Messmer has claimed to be the creator of 'Felix', stating he solely created the cat's actual first cartoon, 'Feline Follies'. The discussions on this matter last to this very day.