Sheppard completed his graduation from the Royal Academy of Dramatic Art in 1958. He spent 12 years of his life as an Associate Artist with the Royal Shakespeare Company. He made his film debut in 1966 with the film Marat/Sade and since then been a regular feature in films and Television shows. He won lot of appreciation for The Homecoming in the year 1995, at the Matrix Theatre. His role also won him the Los Angeles Drama Critics Circle Award.
He starred in many episodes of different series of Max Headroom and Star Trek, He also featured in films Star Trek VI: The Undiscovered Country and lately in 2009 in the reboot Star Trek. He has appeared in two roles on the science fiction series Babylon 5 and then in The Long Twilight Struggle. Sheppard was applauded for portraying the role of Captain Archibald Witwicky in the live action film Transformers. Till date he has acted in some 50 films. He lent his voice in the famous computer game Civilization 5.
His Son Mark Andreas Sheppard is also a renowned Actor.