Nesbitt got his breakthrough television role playing Adam Williams in the romantic comedy-drama Cold Feet (1998–2003), which won him a British Comedy Award, a Television and Radio Industries Club Award, and a National Television Award. His first significant film role came when he appeared as pig farmer "Pig" Finn in Waking Ned (1998). With the rest of the starring cast, Nesbitt was nominated for a Screen Actors Guild Award. In Lucky Break (2001), he made his debut as a film lead, playing prisoner Jimmy Hands. The next year, he played Ivan Cooper in the television film Bloody Sunday, about the 1972 shootings in Derry. A departure from his previous "cheeky chappie" roles, the film was a turning point in his career. He won a British Independent Film Award and was nominated for the British Academy Television Award for Best Actor.
Nesbitt has also starred in Murphy's Law (2001–2007) as undercover detective Tommy Murphy, in a role that was created for him by writer Colin Bateman. The role twice gained Nesbitt Best Actor nominations at the Irish Film & Television Awards (IFTA). In 2007, he starred in the dual role of Tom Jackman and Mr Hyde in Steven Moffat's Jekyll, which earned him a Golden Globe Award nomination in 2008. Nesbitt has since appeared in several more dramatic roles; he starred alongside Liam Neeson in Five Minutes of Heaven (2009), and was one of three lead actors in the television miniseries Occupation (2009). He also starred in the movies Outcast (2010) and The Way (2011).
Nesbitt is married to former actress Sonia Forbes-Adam (who portrayed as Belladonna Took in An Unexpected Journey) with whom he has two daughters, Peggy and Mary Nesbitt (who also appeared in the film series). He is an advocate of numerous charities, and in 2010 he accepted the ceremonial position of Chancellor of the University of Ulster.