Darrow was born in Surrey, England, and attended Haberdashers' Aske's Boys' School before studying at the Royal Academy of Dramatic Art.

The popularity of his role as Avon has tended to overshadow his extensive work in theatre and television. He also plays the character of Kaston Iago in the Kaldor City audios. He appeared in all but the first episode of Blakes 7. In the final episode of the series, in which all of the main characters are seen to be shot, Avon shot dead the character Klyn - played by Paul Darrow's wife, Janet Lees Price.

Darrow's other notable TV appearances include: Emergency Ward 10, The Saint, Z Cars, Dixon of Dock Green, Within These Walls, as the Sheriff of Nottingham in the 1975 BBC series The Legend of Robin Hood, as Mr. Tallboy in the 1973 TV adaptation of Dorothy L. Sayers' Murder Must Advertise, as Thomas Doughty in the TV film Drake's Venture, Dombey and Son, Maelstrom, Making News, Pie in the Sky,Hollyoaks and Little Britain. He spoke the voiceover for Biblical quotations in Richard Dawkins'sThe Root of All Evil?.

Proud of his work on Blake's 7, Darrow has acted as the show's most prolific spokesperson, both in the UK and during the late 80s, in the U.S., when the show was frequently broadcast on US public television. In the mid to late 1990s, he has also purchased the rights to Blake's 7 and attempted to produce a big-budget followup miniseries, Blake's 7: A Rebellion Reborn. According to Darrow, it would have begun 25 years after the ending of the original series and might have included an aged Avon passing the torch to a new generation.

Darrow records voiceovers and straplines for Jack FM, a radio station based in Oxford, Oxfordshire, United Kingdom, Jack FM Hertfordshire, and 106 Jack FM . He also provides the voice of the character Grand Moff Tarkin in the computer game Empire at War. Darrow appeared in Emmerdale from 13 July 2009, playing Eddy Fox, a friend of Alan Turner's; he knows Turner as "Tank".

He is the author of A Terrible Aspect (ISBN 0-80651-112-5), a 1989 novel about Avon's father and Avon's own early life. Darrow's autobiography, You're Him, Aren't You? (ISBN 1-84435-236-6) was published in 2006.