Henry first appeared on stage as a footman in amateur dramatic society Highcliffe Charity Players' production of Cinderella at age 11. He is now the president of HCP and continues to support their productions.
In 1987, Henry appeared in the episode "Rumpole and the Official Secret" from Season 4 of Rumpole of the Bailey. In the early 1990s, he played the acerbic, demonic Dr Walpurgis in The Vault of Horror, a BBC Halloween special. His make-up was provided by Hellraiser veteran Geoff Portass. Henry also introduced a few series of cult horror films in several BBC One Friday night horror seasons, with scripted introductions written by horror novelist and film historian Kim Newman. He appeared in the 1996 schools series Look and Read: Spywatch, and in ITV's 1996 adaptation of Emma. In 1998 he appeared in the medical soap opera Peak Practice, and in two episodes of The Grand.
2000 onwards
He appeared in four episodes of the 2001 series of the medical soap Doctors. He has also frequently been cast as a conspiratorial and/or Machiavellian civil servant, as in Fields of Gold and Foyle's War. He played the title role in Channel 4's 2004 documentary Who Killed Thomas Becket? ; and was a deportment tutor and a shoemaker respectively in the BBC's adaptation of The Young Visiters and Sherlock Holmes and the Case of the Silk Stocking. He played the part of Corporal Ludovic in the C4 presentation of Evelyn Waugh's Sword of Honour trilogy alongside the then relatively unknown Daniel Craig. In 2004 he appeared in Waking the Dead series 3 "Multistorey" as Guy Reynolds. In 2005 he appeared in the feature-length ITV drama Colditz and had a recurring role in Extras, which continued into a few episodes of the comedy's second season. He also had a small role in the ITV drama, Trial & Retribution IX: The Lovers. His main role that year, however, was as Cassius in the last two or three episodes of the first series of HBO/BBC series Rome. He reprised this role in the second series until the character's death at the Battle of Philippi in the episode Philippi. His friend Sarah Kennedy commented that this was a natural progression for one with his "lean and hungry look". In 2006, he played a lawyer in Midsomer Murders, appeared with Michael Sheen in , and featured in the first, fifth and sixth episodes of the first series of The Chase. In 2007 he appeared as the UK's UN Ambassador in The Trial of Tony Blair and appeared in the seventh episode of the second series of Hotel Babylon. Also in 2007 he appeared on radio as Noël Coward in the Afternoon Play of 4 May 2007, "The Master and Mrs Tucker" by Roy Apps, which told of Coward's friendship with Edith Nesbit. In 2008, he appeared in HBO's John Adams as Jonathan Sewall, Massachusetts's Attorney General, as Mr Collins in Lost in Austen, and in Series 7, Episode 4 of Spooks. In 2009 he appeared in Margaret and in Lewis. Also in 2009 he appeared in several episodes of Ricky Gervais' BBC comedy Extras as the commissioning editor of BBC Comedy. In 2010 he appeared as a lawyer in an episode of The IT Crowd titled "Something Happened". In October 2010 he joined the regular cast of Holby City as surgeon Henrik Hanssen, a role he played for three years until his departure in October 2013. In October 2014, it was announced that he would rejoin the cast of Holby City. In October 2014, he appeared as the inspector in the BBC 6-part drama Our Zoo. In January 2015, he appeared as hypnotist Arthur Welkin in the BBC series Father Brown episode 3.3 "The Invisible Man". In October 2016, he appeared as Mr Murthwaite in the BBC mini-series The Moonstone. In November 2017, he appeared as the Dean of Westminster in the second season of the Rainmark Films series The Frankenstein Chronicles.
Film
Henry's film credits include appearances in Another Country with Rupert Everett, Lady Jane, England, My England film by Tony Palmer, in Stephen Fry's 2003 film Bright Young Things as Archie Schwert, in V for Vendetta as Conrad Heyer, in Starter for 10 as a university professor, in Expresso, in Vincente Amorim's 2008 film Good as a senior doctor in Nazi Germany and as Pius Thicknesse in Harry Potter and the Deathly Hallows – Part 1 and Part 2. In 2014, he appeared in the critically acclaimed short film Done In. In 2016, Henry appeared in Rogue One: A Star Wars Story, providing the physical and vocal performance for Grand Moff Tarkin; the use of CGI special effects recreated the likeness of Peter Cushing, who died in 1994, for the character.
From around 2004 until the end of her show in 2010, Guy Henry gained an additional fanbase as a result of his friendship with the Radio 2 presenter Sarah Kennedy, who began by corresponding with his father. Through letters to Sarah from Henry himself, his father and "the Lady Agrippa", listeners were kept up to date on his career. A recording of his voice announced her regular "It's Showtime!" slot of tunes from the musicals at about 6.45am GMT – originally he, and a whole repertoire of different recordings was later added. He also occasionally appeared live on her show, and co-hosted with her as part of the annual charity appeal Children in Need.
Guest appearances
Henry was a guest speaker at an NEH summer seminar entitled Shakespeare: Enacting the Text..
