For most of World War II, Ellis was absent from the theatre, performing welfare work in hospitals, and from time to time giving concerts to entertain members of the armed forces. Returning to the stage after the war, Ellis was successful in the 1944 and 1947 British productions of Noël Coward's melodrama "Point Valaine", playing a hotel keeper in a sordid, clandestine relationship with her head waiter. In 1948 she gave one of her most praised performances as the embittered Millie Crocker-Harris in Terence Rattigan's "The Browning Version". In 1952 she played Volumnia in Coriolanus for the nine-month Stratford season.