In 2000, Hunnam made his US television debut with a recurring role on the teen drama "Young Americans" on The WB. From here he landed a regular role on the Fox sitcom "Undeclared" (2001-2002), a college-set series created by Judd Apatow of the critically acclaimed but short-lived series "Freaks and Geeks". The charm of "Undeclared,” like its series predecessor, was in the details and the fully-formed characters. Hunnam's Lloyd, a theater major with an eye for the ladies, was a surprisingly atypical character. The actor's fresh-faced charm and confident swagger lent Lloyd a believable edge while the writing helped to elevate the series and its primaries above typical teen stereotypes.

Hunnam made his first leap to film in 1999 with a role as a rock singer in the British comedy "Whatever Happened to Harold Smith?" (released in the US in 2001). He made his US feature debut opposite Katie Holmes in the thriller "Abandon" (2002) and finished the year starring in the feature drama based on the Charles Dickens' novel "Nicholas Nickleby,” in which he played the resourceful 19th century lad whose comfortable life is suddenly upended after the tragic death of his father leaves him and the rest of his family penniless, and at the mercy of his wicked Uncle Ralph (Christopher Plummer). He made the most of his limited screen time in “Cold Mountain” (2003), playing a member of the Home Guard, a group of Civil War marauders who find and kill deserters for cash. In the ultra-violent sports drama, “Green Street Hooligan” (2005), he played a charming and dangerous English thug who takes an American (Elijah Woods) expelled from Harvard under his wing and teaches him the finer points of football (not soccer) hooliganism.