His first major role was on the TV series The Commish where he played Officer Enrico Caruso from 1991 to 1994. It was during this time that he had a minor guest role in a first-season episode of The X-Files called Genderbender.The producers were impressed by his performance and when, in the second season, he auditioned for the role of turncoat FBI agent Alex Krycek, he was successful. Lea guest starred in eleven episodes from 1994 to 1996 and became a popular character amongst the fans. Because of his character's willingness to switch sides, he was known as the 'ratboy'. In the season three episode Apocrypha, Krycek was left to die in an abandoned silo with an alien ship.This allowed Lea to take a starring role in the series Once a Thief - which followed on from the 1996 John Woo film - alongside Ivan Sergei. The series was cancelled after one season, but Lea only had to come knocking and the producers welcomed him back to The X-Files, as did the fans. Lea continued to play Krycek, who quickly became a nemesis not just of Mulder and Scully but particularly of A.D. Skinner (Mitch Pileggi). In various capacities, Lea continued appearing on the show until its end in 2002.As of 2006, Lea has a recurring role on Kyle XY and the Canadian TV series Whistler.