Cleveland worked on the HBO original series Six Feet Under throughout the show's five season run. Cleveland joined the crew as a writer and producer for the show's first season in 2001. He wrote the episode "The Trip". He was promoted to supervising producer for the second season in 2002. He wrote two further episodes – "Driving Mr. Mossback" and "The Liar and the Whore". He remained a supervising producer for the third season in 2003. He scripted two more episodes – "Nobody Sleeps" and "Death Works Overtime". He was promoted to co-executive producer for the fourth season in 2004. He wrote two more episodes – "In Case of Rapture" and "Grinding the Corn". He was promoted again to executive producer for the fifth and final season in 2005 and wrote his last episode, "Eat a Peach". He wrote eight episodes in total for the series.
Cleveland won the Jury Award for Best One Person Show at the 2006 US Comedy Arts Festival in Aspen, Colorado for his performance in "My Buddy Bill", about his fictional friendship with President Bill Clinton, a monologue play filmed on June 15, 2007 for a Comedy Central Special and DVD.