Bainbridge made her professional debut as the Third Lady in "Die Zauberflöte" at Glyndebourne in East Sussex in 1963. The following year saw her debut at the Royal Opera House in Wagner's "Die Walküre". She joined the company in 1965, and appeared at Covent Garden more than a thousand times: among her roles were Amneris, Arvidson, Auntie (in "Peter Grimes"), Berta, Emilia, Erda, Grandma Burya, Mamma Lucia, Mistress Quickly and Suzuki. She sang in concert in the Barbican Hall, the Royal Festival Hall and the Royal Albert Hall, starring twice in the Last Night of the Proms with Colin Davis.