The sixth season of the American comedy television series It's Always Sunny in Philadelphia premiered on FX on September 16, 2010. It is the first season of the show to be filmed in high-definition. The season contains 14 episodes and concluded airing on December 16, 2010, with the hour-long Christmas special. An additional episode called "The Gang Gets Successful" was produced for this season, but was not aired, despite scenes from the episode being included in promotional material for season 6. It was later re-edited with new scenes to create the season 7 episode "How Mac Got Fat".

Charles Peckham Day is an American actor, writer, producer, and podcaster. He is best known for playing Charlie Kelly on the FX comedy It's Always Sunny in Philadelphia (2005–present), which he stars in with Rob McElhenney and Glenn Howerton, and of which he is also a writer and an executive producer. In 2011, he was nominated for a Critics' Choice Television Award and a Satellite Award for the role. He subsequently co-created the Fox sitcom The Cool Kids (2018–2019) with Paul Fruchbom and the Apple TV+ comedy Mythic Quest (2020–present) with Rob McElhenney and Megan Ganz, and continues to executive-produce the latter.