His credits include three appearances in Doctor Who (1968, 1972 and 2015), The Black Panther (1977), Bleak House (1985), The Queen's Nose (1995–1998), Great Expectations (1999), Nicholas Nickleby (2001), Enigma (2001), K-19: The Widowmaker (2002), The Constant Gardener (2005), Being Human (2009–2010), Ultramarines: The Movie (2010), Black Mirror (2011), Game of Thrones (2011–2012), Endeavour (2018), Les Misérables (2018), and Chernobyl (2019).

[3] Sumpter also appeared in many television films and serials, including adaptations of Dickens' novels: Nicholas Nickleby in 2001,[2] Great Expectations in 1999,[2] and Bleak House in 1985.

He took the role of Alexander Bonaparte Cust in the 1992 Agatha Christie's Poirot adaptation of The ABC Murders.

He has also appeared in episodes of Midsomer Murders, The Bill, Holby City, Black Mirror, and A Touch of Frost.

[4] He played Harold Chapple in Our Friends in the North, and portrayed the physicist Max Planck in Einstein and Eddington.