Collier was only three when she made her stage debut in 1881 as Peaseblossom in A Midsummer Night's Dream. She was once a show girl--one of the popular "Gaiety Girls"--but she wanted to play more serious parts, so she joined Herbert Beerbohm Tree's company and started playing in most of his important productions, many of them Shakespeare's plays, from 1901 until 1908. She made her New York debut in 1908 and then played both sides of the Atlantic with equal popularity and success. One of her critical triumphs was as Gertrude in John Barrymore's London production of Hamlet. She published her memoirs Harlequinade in 1929.