Joe Armstrong is an English actor, best known for his roles in the television series Robin Hood, Happy Valley, and The Village. He has also starred in films such as Darkest Hour and The Hollow Crown.

Armstrong was born in Hammersmith, London, England, in 1978. He is the son of actor Alun Armstrong. He has an older brother, Tom, and a younger brother, Dan, who was in the band Clock Opera. He attended Elliott School in Putney from 1993 to 1997. He then studied at the University of Bristol, where he acted in The Brecht Project—a collection of scenes from the works of Bertolt Brecht—in 1998 and Women Beware Women in 1999.

Armstrong's first major television role came in 2006, when he was cast as Allan A Dale in the BBC series Robin Hood. He remained with the series for all three seasons, which aired from 2006 to 2009.

In 2014, Armstrong starred in the BBC series Happy Valley as Ashley Cowgill, a police officer who is investigating a murder in a small Yorkshire town. The series was a critical and commercial success, and Armstrong's performance was praised by critics.

In 2017, Armstrong starred in the BBC series The Village as Bairstow, a newcomer to a small English village who is hiding a dark secret. The series was also a critical and commercial success, and Armstrong's performance was praised by critics.

Armstrong is currently filming the upcoming television series The Undeclared War, a six-part thriller series for Channel 4. He will play the role of Daniel Granger, a computer analyst who is recruited by the government to help with a cyberwarfare operation.