She is best known for her role in the British television comedy series Brass and to international audiences as Mon Mothma in the Star Wars film Return of the Jedi, and Aunt Agatha in Poldark.

She portrayed Mon Mothma, the primary political leader of the Rebel Alliance in the 1983 Star Wars film, Return of the Jedi.

The 1980s saw Blakiston in a lead role as head of a special unit within British intelligence, opposite Alec McCowen in Mr. Palfrey of Westminster.

She and Geoffrey Palmer (Lionel) had previously played estranged spouses a decade earlier in Carla Lane's series The Last Song.

In 1970, Blakiston married the actor Russell Hunter after they had played together in A Midsummer Night's Dream at the Open Air Theatre, Regent's Park.