He is best known for playing the character of Don Danbury in the BBC Three series How Not to Live Your Life which he wrote and starred in.Clark's first television appearance was in a December 1996 episode of Only Fools and Horses.
In 1999 Clark wrote and appeared in an episode of the second series of Comedy Lab on Channel Four entitled "Roy Dance Is Dead" which aired on 16 September, 1999. He appeared as the character Jerry Zachery. From that he co-wrote the comedy series The Estate Agents which aired on Channel Four in 2002. He again appeared as the character of Jerry Zachery. In 2003 he appeared in the British sitcom, Mad About Alice as Jason and in 2004 he appeared as Johnny Two Hats in an episode entitled "Electro" of the first series of the comedy television show The Mighty Boosh. The same year he had a guest appearance in French & Saunders and in the 2005 Christmas Special of My Family'.
In 2006 Clark appeared in the ITV comedy drama series The Complete Guide to Parenting. He was also commissioned to write two short comedies for Paramount Comedy 1 - Dan Clark's Guide to Dating and Dan Clark's Guide to Working both of which he co-wrote with Gary Reich. Clark was the main character in both shows and Isabel Fay appeared in Dan Clark's Guide to Dating which was shown as ten one-minute clips on the channel, with lists of ten things people shouldn't do on a date, such as "Ten things you shouldn't wear on a date". The clips began to appear on the Internet and the BBC approached him about doing a 30 minute show in the same format. The result was the pilot for How Not to Live Your Life, using the same style of short clips within a traditional sitcom. The pilot aired on BBC Three on 27 September, 2007. The BBC then commissioned a full series which aired on BBC Three in August and September 2008. Clark wrote each episode and directed four episodes.