Diana Montague was born in Winchester and educated at the Testwood School, the Winchester School of Art and the Royal Northern College of Music. She made her professional debut as Zerlina in Don Giovanni with Glyndebourne Touring Opera in 1977 and went on to sing leading mezzo-soprano roles in opera houses throughout Europe and as well as in the United States. She made her Metropolitan Opera debut as Annio in La clemenza di Tito on 22 January 1987 and later appeared with the company as Sesto in La clemenza di Tito (1987), Dorabella in Così fan tutte (1988), Cherubino in Le nozze di Figaro (1988), Nicklausse in Les contes d'Hoffmann (1989) and in 2016 she returned after a 27-year absence to sing Gertrude in Roméo et Juliette. In 2013 she sang at Opera Holland Park as Carmela in I gioielli della Madonna by Wolf-Ferrari.

Montague is married to the British tenor David Rendall.