According to Official Guinness Records,
The fastest marathon dressed as Elvis is 2 hr 42 min 52 sec by Ian Sharman(UK) at the 2009 Seattle Marathon in Washington, USA, on 29 November 2009.
Ian crossed the finish line wearing a high-rise pompadour wig and a white jumper suit. He managed to reclaim the title he previously held in 2008.
For a complete list of 2009 records, please visit 2009 Guinness Records in United States.