William James Nesbitt (born 15 January 1965) is an actor from Northern Ireland.

From 1987, Nesbitt spent seven years performing in plays that varied from the musical Up on the Roof (1987, 1989) to the political drama Paddywack (1994). He made his feature film debut playing talent agent Fintan O'Donnell in Hear My Song (1991). He got his breakthrough television role playing Adam Williams in the romantic comedy-drama series Cold Feet (1997–2003, 2016–present), which won him a British Comedy Award, a Television and Radio Industries Club Award, and a National Television Award.

Nesbitt's first significant film role came when he appeared as pig farmer "Pig" Finn in Waking Ned (1998). With the rest of the starring cast, he 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, 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 (2010). He portrayed Bofur in The Hobbit film series (2012–2014). In 2014, Nesbitt starred as Tony Hughes in the acclaimed BBC One drama series The Missing.