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 productions 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 local caravan park owner and drug dealer involved in a high-stakes kidnapping plot. The series was a critical and commercial success, and Armstrong's performance was praised by critics.

In 2013, Armstrong starred in the BBC series The Village as Stephen Bairstow, a deeply traumatized war veteran returning home to a changing rural community. The series was also a critical and commercial success, and Armstrong's performance was praised by critics.

Armstrong also starred in the 2022 television series The Undeclared War, a six-part thriller series for Channel 4. He played the role of Daniel Granger, a veteran GCHQ analyst overseeing a critical cyberwarfare operation during a national crisis.

In his recent work leading up to 2026, Armstrong has continued to secure prominent roles on British television and stage. He appeared in the crime drama The Bay (2023) and the global Netflix hit Fool Me Once (2024), followed by performances in the historical drama A Cruel Love: The Ruth Ellis Story (2025) and the thriller series The Blame (2026). Additionally, he returned to the stage to star in the acclaimed National Theatre production of London Tide (2024).