Alexander Armstrong was born 2 March 1970 in Rothbury, Northumberland, England. He is the youngest of three children of Henry Angus Armstrong, a physician, and Emma Virginia Thompson-McCausland, whose family has Irish aristocratic connections.

He first gained recognition in the 1990s as part of the comedy partnership Armstrong and Miller with Ben Miller, appearing in the sketch series The Armstrong & Miller Show. His quick wit and comedic timing led to roles in acting, voice work, and television presenting.

Armstrong became widely known as the long-time host of the BBC Relationshipsquiz show Pointless on BBC One, which he has presented since its debut in 2009. He has also presented documentaries and entertainment programmes including The Great British Weather (BBC One), Epic Win (BBC One), and travel series such as Alexander Armstrong in the Land of the Midnight Sun (ITV).

Alongside television, Armstrong presents a weekday morning show on Classic FM, demonstrating his passion for classical music.

He lives in Gloucestershire with his wife, Hannah Snow and children and frequently speaks about the importance of family life alongside his busy broadcasting career.