Thomason first came to prominence on British television in the fifth series of Pie in the Sky (1997) playing the waitress, Sally, in eight episodes.

She starred in the U.S. television series Las Vegas as Nessa Holt in seasons one and two, a total of 47 episodes.

In August 2008, Thomason was cast as a series regular in the CW show Easy Money.

[3] After appearing in the pilot episode for White Collar as agent Diana Berrigan, she returned for the first-season finale.

Being a friend of Dominic Monaghan (who played Charlie Pace on the series), she was a huge fan of the show and excited to be cast.