Mardle was runner-up in three PDC majors, losing to Phil Taylor on each occasion. He was also a five-time world semi-finalist. 

He has been known as "Hawaii 501" since 2000, a play on the title of the popular television series Hawaii Five-O, due to the Hawaiian shirts he started wearing in 1998 for a bet, and 501 being the start score of a leg of darts. Mardle is one of the most popular players on the circuit.