Winning first prize in the 1974 ARD Competition, singing Purcell and Bach in the final, launched Marshall's international career that initially focussed on the concert platform.
She then participated in the series of recordings of Vivaldi's complete sacred vocal music with the English Chamber Orchestra conducted by Vittorio Negri.
The Italian conductor invited her back to Florence for his first production Le Nozze di Figaro in 1979, in which she sang the role of the Countess.
Other roles include Violetta (La traviata), the Marschallin (Der Rosenkavalier), the Countess (Capriccio), Lucio (Tito Manlio), and Hypernmestre (Salieri's Les Danaïdes).
She recorded the St Matthew Passion with Michel Corboz and the Orchestre de Chambre de Lausanne, Jephtha with Sir Neville Marriner and the Academy of St Martin in the Fields for Decca Records, Handel's Messiah and Dixit Dominus with John Eliot Gardiner and the English Baroque Soloists for Philips Records, Bach's Mass in B minor with Sir Neville Marriner and Pergolesi's Stabat Mater with Claudio Abbado conducting the London Symphony Orchestra for Deutsche Grammophon (featuring Lucia Valentini Terrani as the contralto soloist).