After further engagements with Gothic Voices and other groups he made his professional opera debut in 1988 as Armindo in Scarlatti's Gli equivoci nel sembiante at Innsbruck's Early Music Festival.
Other notable concert appearances include performances with the London Philharmonic under Roger Norrington, the London Symphony under Sir Colin Davis, Mstislav Rostropovich and André Previn, Les Musiciens du Louvre under Marc Minkowski, the Cleveland Orchestra under Franz Welser-Möst, the New York Philharmonic under Kurt Masur, the Boston Symphony under Seiji Ozawa, the San Francisco Symphony under Jeffrey Tate, the Vienna Philharmonic under Trevor Pinnock, the Academy of St Martin in the Fields under Neville Marriner, and both the Orchestra of the Maggio Musicale Fiorentino and the Orchestre de Paris under Carlo Maria Giulini among many others.
[1] More recently, Ainsley has sung the roles of Soliman in Zaide and Belfiore in La finta giardiniera at the Salzburg Festival (2006), The Madwoman in Britten's Curlew River with Oper Frankfurt (2006), Pelléas in Pelléas et Mélisande with the Deutsche Oper Berlin (2006), Skuratov in Janáček's From the House of the Dead with both the Amsterdam and Vienna Festivals (2007), Hippolyt in the world premiere of Henze's Phaedra with the Berlin State Opera (2007) and La Monnaie (2007), Vere in Billy Budd with Oper Frankfurt (2007), Chevalier de la Force in Dialogues des Carmelites with the Hamburg State Opera (2008), and both Bajazete in Tamerlano and the title role in Idomeneo with the Bavarian State Opera (2008).
Ainsley has also become particularly associated with Handel's music and has recorded over ten of his oratorios including Jephtha, La Resurrezione, Messiah, Joshua and Saul.
He has also recorded numerous English and French songs including works by Ralph Vaughan Williams, Peter Warlock, Herbert Howells, Gerald Finzi and Gabriel Fauré among others.