He appeared in 11 productions of the National Youth Theatre in five seasons between 1974 and 1978, and began carving a successful career as a stage actor in the 1980s, alongside various television roles.

After playing several minor roles in other Hollywood films such as White Hunter Black Heart (1990) and Alien 3 (1992), Mantle was cast as consultant Dr Mike Barratt in Casualty, becoming one of its most popular characters.

In 2003 he appeared in Rattle of a Simple Man; in 2006 he played the part of The Narrator in The Rocky Horror Show; and over the Christmas and New Year period of 2007–2008, he portrayed the villain Abanazer in a pantomime production of Aladdin at the Theatre Royal in Bath.

More recently, Mantle has become known for his roles on television as Lord Greatjon Umber in HBO's Game of Thrones and as Tony Curry, Ollie's (Will Mellor's) father, in the BBC's White Van Man.

[5] He trained at the Royal Academy of Dramatic Art (RADA) between 1978 and 1980,[3] where he initially found his towering height of 6' 5½" (1.97 m)[6] to be a hindrance to the sort of roles he could convincingly perform in his acting.

[7]In 1980, Mantle debuted on the screen with a small role as Ewen in Christian Marnham's short thriller feature The Orchard End Murder.

From 3 November 1982, Mantle portrayed Jurgen opposite Eamon Boland, C. J. Allen, Philip Donaghy and Ian McCurrach in David Hayman's award-winning stage production of Coming Clean at the Bush Theatre in London.

Footage for the series was shot in rural Somerset and Wiltshire, with the Saxon Tithe Barn in Bradford-on Avon functioning as the great hall of Nottingham Castle, Great Chalfield Manor near Melksham doubling as Maid Marion's family home, and numerous battles were shot at Leaford Grange and Nettleton Mill near Castle Combe, locations which Mantle considered to be "wonderfully realised and breathtaking".

[3][15] Other theatrical credits include The Relapse; The Red Devil Battery Sign; King John; Johnny Johnson; The Ideal Gnome Expedition; East; Blood on the Neck of the Cat and Bedroom Farce.

In 1986, Mantle replaced Alan Rickman as Achilles in Howard Davies's Royal Shakespeare Company production of Troilus and Cressida at the Barbican Theatre in London.

"[18] He continued with minor screen roles as a ruffian on a bus in Ronald Neame's film Foreign Body and as "Big Ben" Davis in Dempsey and Makepeace in 1986.

[15] In 1990, Mantle had a small role as an electricity meter reader in the One Foot in the Grave episode "The Return of the Speckled Band", and played Harry, a man who "gave Clint Eastwood a pounding" in White Hunter Black Heart.

[26]In 1995, Mantle was honoured with a surprise This Is Your Life edition, presented by Michael Aspel; the title theme drew upon the "Robin of Sherwood", after his role as Little John.

[32] Mantle was a friend of Jill Dando, and played the prosecuting barrister in a TV dramatisation of the trial of Barry George in a Tonight With Trevor McDonald special, Nothing But The Truth.

[3][37] Ian Shuttleworth of the Financial Times describes Mantle's Victor as a character who "sacrificed a promising academic career in science to become a cop on the beat simply in order to keep his shattered father" and said that "Clive Mantle expresses his obstinacy through gritted teeth and cold, civil smiles rather than letting it loose", also remarking that both he and his wife Esther (played by Susan Wooldridge) seemed several years too young for their roles.

[38] After experiencing mixed fortunes in his acting career after leaving Casualty,[39] Mantle agreed to return to the role as Dr Mike Barratt in Holby City in 1999.

That year, Mantle participated in a charity trek of the Annapurna circuit in the Himalayas and to Everest Base Camp, reaching 18,420 ft in aid of Hope and Homes for Children.

In 2003, Mantle played Maynard in Ben Bolt's TV movie, Second Nature, which starred Alec Baldwin in the leading role, and appeared in the first episode of the series Fortysomething.

[15] He portrayed Percy, described as a "big, bashful Northern mill-worker who lives with his mum", in Patrick Sanford's stage production of Rattle of a Simple Man at the Clwyd Theatr Cymru in Mold, Flintshire.

Gail Cooper of the Western Mail praised his performance and said: Mantle, better known as dishy and confident consultant Mike Barrett in Casualty, is cast completely against type as Percy, the 42-year-old virgin who admits to being only 35.

His body language is superb: awkward, self-effacing, obsessively tidy – Coronation Street fans should think Roy Cropper if they want to imagine the sort of man Percy is.

[43] During production, Mantle fell on his face while shooting a fencing scene and was rushed to Selly Oak Hospital with a ruptured ligament in his leg.

In 2006, he guest-starred in the Doctor Who audio drama The Settling by Big Finish Productions, and had a role in Simon Shore's TV movie about a boy with autism, After Thomas, He toured as "The Narrator" in The Rocky Horror Show, and also played Brauner opposite Robin Hood's Michael Praed in Haymarket Productions's National Tour of Brian Stewart's Killing Castro.

[14] The play was performed at the Festival Theatre in Malvern in June 2006, and was described by the Birmingham Mail as an "acclaimed comedy" which "chronicles the more bizarre of America's attempts to kill the Cuban leader Fidel Castro – including filling his shoes with poison and inventing an exploding cigar.

[47] Mantle was thrilled to take on the role as Cooper is his ultimate comic hero, saying "It's such a big privilege playing Tommy – I genuinely love the man.

"[3][14][47] Mantle considered the role highly challenging, given that he had to combine several aspects of skill, from the magic tricks to the joke-telling, the physical comedy, and emulating the distinctive voice.

[50] He also has an ongoing role in HBO's Game of Thrones as Lord Greatjon Umber, a close ally of Robb Stark, and has provided the voice to the audio editions of Andy McNab's Nick Stone thrillers.

[citation needed] In 2014, Mantle supplied the voice of Gator in the eighteenth season of the British children's television series Thomas & Friends as well as its sixth CGI animated film Tale of the Brave.