Parkhouse has been in comics since 1969, when he co-wrote two Marvel Comics stories, one starring the jungle lord Ka-Zar in Marvel Super-Heroes #19 (March 1969), and the other starring the eponymous superspy in Nick Fury, Agent of S.H.I.E.L.D. #12 (May 1969).

Since then he has worked on a wide range of titles from 2000 AD to Warrior and various Marvel UK titles.

His best known work includes Big Dave (with Mark Millar and Grant Morrison) in 2000 AD, The Bojeffries Saga with Alan Moore, Night Raven with David Lloyd and various strips in Doctor Who Magazine. He was the writer of the Doctor Who strip from 1981—1985, and illustrated three episodes in 1982-83.

In 2004 he provided the art for Angel Fire, which was written by Chris Blythe (better known for his colouring work). This was published by Shattered Frames, a company they established in the same year to produce British graphic novels. In the same year he also drew the Joe Casey-written mini-series Milkman Murders, published by Dark Horse.

He is married to fellow letterer Annie Parkhouse.

Comics work includes:

• Night Raven (with David Lloyd, Marvel UK, 1979)
• Black Knight (with artists John Stokes and Paul Neary, in Hulk Weekly #1-60, Marvel UK, 1979—1980)

• Doctor Who:
• Fourth Doctor (collected in Dragon's Claw, Panini, 164 pages, 2005, ISBN 1904159818):
• "The Deal" (with Dave Gibbons, in Doctor Who Magazine #53)
• "End of the Line" (with Dave Gibbons, in Doctor Who Magazine #54-55)
• "The Freefall Warriors" (with Dave Gibbons, in Doctor Who Magazine #56-57)
• "Junkyard Demon" (with Mike McMahon/Adolfo Buylla, in Doctor Who Magazine #58-59)
• "The Neutron Knights" (with Dave Gibbons, in Doctor Who Magazine #60)
• Fifth Doctor (collected in The Tides of Time, Panini, 212 pages, 2005, ISBN 1904159923):
• "Tides of Time" (with Dave Gibbons, in Doctor Who Magazine #61-67)
• "Stars fell on Stockbridge" (with Dave Gibbons, in Doctor Who Magazine #68-69)
• "The Stockbridge Horror" (with Mick Austin, in Doctor Who Magazine #70-75)
• "Lunar Lagoon" (with Mick Austin, in Doctor Who Magazine #76-77)
• "4-Dimensional Vistas" (with Mick Austin, in Doctor Who Magazine #78-83)
• "The Moderator" (with Steve Dillon, in Doctor Who Magazine #84 and 86-87)
• Sixth Doctor (with John Ridgway, collected in Doctor Who: Voyager, Marvel Comics, 100 pages, 1989, ISBN 1854000454):
• "The Shape-Shifter" (in Doctor Who Magazine #88-89, 1984)
• "Voyager" (in Doctor Who Magazine #90-94, 1984)
• "Polly the Glot" (in Doctor Who Magazine #95-97, 1984)
• "Once Upon a Time-Lord..." (in Doctor Who Magazine #98-99, 1984)

• The Bojeffries Saga (with Alan Moore, in Warrior #12, 13, 19 & 20, 1983—1984; Dalgoda #8, Fantagraphics Books, 1986; A1 #1-4, A1 True Life Bikini Confidential, Atomeka Press, 1989—1990; collected edition, Tundra, 1992, ISBN 1879450658)

• Moonrunners: "Moonrunners" (co-written with Alan McKenzie, with art Massimo Belardinelli, in 2000 AD #591-606, 1988)

• The Spiral Path (script and pencils, with inks by John Ridgway, Warrior #1-12, 1982—1983)

• Big Dave (written by Grant Morrison and Mark Millar):
• "Target Baghdad" (in 2000 AD #842-845, 1993)
• "Young Dave" (in 2000AD Yearbook 1994, 1993)
• "Monarchy in the UK" (in 2000 AD #846-849, 1994)
• "Wotta Lotta Balls" (in 2000 AD #904-907, 1994)

• The Journal of Luke Kirby (with Alan McKenzie):
• "Sympathy for the Devil" (in 2000 AD #873-877 and #884-888, 1994)
• "The Old Straight Track" (in 2000 AD #954-963, 1995)

• Sandman: The Dreaming: Beyond the Shores of Night (1999, ISBN 1852869046)

• Milkman Murders (with Joe Casey, 4-issue mini-series, Dark Horse Comics, 2004, tpb, 104 pages, 2005, ISBN 1593070802)

• Angel Fire (with Chris Blythe, Shattered Frames, 112 pages, April 2005, ISBN 095499440X, Carlton Books, 192 pages, August 2007, ISBN 1844429180)

1994: Nominated for "Best Graphic Album--Reprint" Eisner Award for The Complete Bojeffries Saga