As a teenager she was noticed riding the London Underground by Director and Producer George Pearson, who cast her in several of his films. In 1918, she made her stage debut in the play Love is a Cottage at the West End theatres Globe Theatre. Encouraged by Gerald du Maurier to change her name to Moyna Macgill (which invariably was misspelled as "MacGill" or "McGill", and on at least one occasion, the film Texas, Brooklyn and Heaven, as "Magill"), she became a leading Actress of the day, appearing in light comedies, melodramas, and classics opposite Herbert Marshall, John Gielgud, and Basil Rathbone, among others.
Angela Lansbury would become a popular stage and film Actress in her own right, starring in the long-running television series Murder, She Wrote after a string of successful musicals spanning between the 1940s and 1960s. In 1935, Edgar Lansbury died of stomach cancer, a year after publishing a biography of his father George. Macgill began an affair with Scotsman Leckie Forbes, a former colonel with the British Army in India. The two moved their respective families to a house in Hampstead, but Macgill soon discovered Forbes' military career had made him a staunch disciplinarian who ruled the household like a tyrant.
In 1942, she was invited to join a troupe that was rehearsing Noël Coward's Tonight at 8:30 for a touring production designed to raise funds for the Royal Canadian Air Force. She accepted, and when the company finished the run in Vancouver, she headed to Hollywood to seek work there. She soon sent for Angela, and eventually the twins, and the family settled in Laurel Canyon.
She died of throat cancer in Los Angeles, just fifteen days shy of her 80th birthday.