Allen Leech (born 18 May 1981) is an Irish actor best known for his role as Tom Branson on the historical drama series Downton Abbey (2010–2015). He made his professional acting debut with a small part in a 1998 production of A Streetcar Named Desire, made his first major film appearance as Vincent Cusack in Cowboys & Angels, and earned an Irish Film & Television Awards nomination in 2004 with his performance as Mo Chara in Man About Dog.

He appeared as Willi in the Queen and Peacock (2000), at the Garter Lane Arts Centre. The following years, he was in The Morning After Optimism (2001) and then Da (2002). His breakthrough film performance was in Cowboys and Angels (2003), followed by a role in the 2004 cross-country caper film Man About Dog. He played the role of Shane Kirwan in Ireland's RTÉ series Love Is the Drug (2004), for which he received a Best Actor nomination from the Irish Film and Television Awards. He followed that up with the role of Willy in the television series Legend (2006), for which he received a Best Supporting Actor nomination from Irish Film and Television Awards.