Perhaps most famous for his role as Dullard on the BBC and HBO series Extras (with Ricky Gervais), Speirs is also known for his portrayal of Andy Fellows on the ITV drama Making Waves and for his performance as Sloan in the 2006 feature film Eragon.
After studying acting at Loughborough University in England, he appeared in episodes of the television series We Are Seven and Goodnight Sweetheart.
For two seasons, he played schoolteacher Gareth Barber on the BBC comedy series Big School.
Born Steven Roberts, he grew up in the village of Troedyrhiw, Merthyr Tydfil, Wales, with a brother named Jeffrey Lloyd Roberts.
He portrayed the late British actor and comedian Bernard Bresslaw in a made-for-TV movie titled Cor, Blimey!