His credits as a writer include Saturday Night Live, Late Show with David Letterman, Late Night with Conan O'Brien, and the Chris Rock Show. He wrote and directed the movie, Pootie Tang, based on a sketch from the latter. His work for the Chris Rock Show was nominated for an Emmy Award 3 times, including winning "Best Writing in a Variety or Comedy Series" in 1999.

As a voice actor he portrayed Brendon's estranged father, Andrew Small, in Home Movies, and appeared numerous times on Dr. Katz, Professional Therapist.

Louis C.K. or Louis Szekely has performed his stand-up frequently on shows like Late Night with Conan O'Brien and the Tonight Show with Jay Leno. Most recently his subject matter reflected his frustrations and anxieties from raising his four-year-old daughter. He was ranked number 98 on Comedy Central's list of 100 greatest standups of all time.

In the spring of 2005, C.K. created, with executive producer Mike Royce, a pilot for a sitcom to be entitled Lucky Louie on HBO. In September -- after doing an August half-hour HBO stand-up special as part of the stand-up series One Night Stand -- he began production on twelve episodes, as the rest of the first season of 13 episodes started airing in June, 2006. The show is filmed in front of a live studio audience; it will be a HBO's first series in that format, and the movie lot being used for taping the first season is the same one where Desi Arnaz made the multi-camera live-audience approach a hallmark of the I Love Lucy show. Lucky Louie is described as a realistic portrayal of family life; some summarize it as "Everybody Loves Raymond with swearing."