Keir was persuaded to take the minor role of a farmer in the play, and enjoyed the experience so much that he later became a regular in the group's performances.

[2][1] The group entered a competition in Inverness, where Keir's talent was spotted and he was offered the chance to become a professional actor at the Unity Theatre in Glasgow.

[2] Since this was after the start of the Second World War, he could not easily leave his occupation as a miner; he was only able to accept the offer after he obtained a medical diagnosis of pneumoconiosis, which freed him from his work in the mine.

[3] Keir made his film debut in 1950 in The Lady Craved Excitement, and performed in his first major screen role in The Brave Don't Cry (1952).

The film concerned the rescue of a group of miners trapped underground after an accident in the pit, with Keir playing a miner who places a bet on a horse race via the mine's telephone system while trapped; he was given the final line of dialogue, as he emerges from the pit following his rescue and asks who won the race.

In 1960 Keir initiated the role of Thomas Cromwell in the original theatrical production of Robert Bolt's play A Man for All Seasons.

[5] In 1964, he was a member of the original West End cast of Lionel Bart's musical Maggie May, playing the trade union leader.

"[1] In 1966, Keir joined the cast list of the second Doctor Who big screen adventure, Daleks' Invasion Earth 2150 A.D., alongside Peter Cushing.

[7] This final performance was praised by The Independent: "This series has so far been hugely enjoyable - thanks in large part to Andrew Keir, who recreates the role of Quatermass in dramatic interludes; lesser actors would treat Kneale's downbeat script with a certain detachment, but Keir is prepared to charge even the most banal lines with a terror that's both a treat and a lesson.