Mary Keegan trained at Rose Bruford. Theatre includes: Rosalind – As You Like It, Viola/Sebastian – Twelfth Night, Roxanne – Cyrano De Bergerac, Lady Macbeth, Duchess – Duchess of Malfi, Gertrude – Hamlet, Belinda – Noises Off, Vi – Memory of Water, Patsy – Perfect Pie, The Girls of Slender Means, Shakespeare Review, Phyllis in American Venus, Man and Superman at The National, Last confessions of a Scallywag at The Mill At Sonning; Thark at The Park Theatre, The Memory of Water for Stellar Quines, Live Like Pigs at The Royal Court, Habeas Corpus, Little Malcolm, Mary Rose, Measure for Measure, The Lion In Winter, and You Never Can Tell – all for Salisbury Playhouse.
Other work includes Audio-Description at the National Theatre, the Coliseum and the Royal Opera House. She also worked with German chanteuse Eva Meier in Just Brecht and Eyes In The Big City.
Television includes East Enders, Father Brown, The Bill, My Hero, Doctors, Ladies of Langham Place, The Mushroom Picker.