On leaving school at 16 he worked briefly on the night shift at the Kellogg's factory in Manchester, but keen to pursue his acting career he soon moved to London.
He appeared in various film and television roles during the 1970s and early 1980s, most notably Soldier & Me, The Mallens and The Siege of Golden Hill, with guest appearances on shows such as Space: 1999 alongside Martin Landau and fellow guest star Patrick Troughton (episode "The Dorcons").
[1] His films included The Black Panther (1977), Meetings with Remarkable Men (1979), Passion Flower Hotel (1978), aka Boarding School, playing Fibs alongside Nastassja Kinski, whom he dated for a while, and the 1979 British disco film The Music Machine.
He played Pip in Great Expectations (1981) and Gringoire in The Hunchback of Notre Dame (1982), and appeared to have a promising career, but after his appearances in The Last Days of Pompeii (1984) and the horror film Don't Open Till Christmas (1984), his career and personal life went into steep decline, with him later developing a drug problem.
On 1 August 1993, Sundquist jumped under a train at Norbiton railway station in England.