Isla Blair made her first stage appearance at the Strand Theatre on 3 October 1963 playing the part of Philia in the London debut of "A Funny Thing Happened on the Way to the Forum". She joined the Royal Shakespeare Company for their 1971 season, during which she portrayed Emilia in "The Man of Mode" and Aglaya in "Subject to Fits". In 1973, Blair toured the Middle East with the Prospect Theatre Company in the role of Viola in "Twelfth Night". Other venues at which Blair has performed include the Old Vic and the Nottingham Playhouse.