Mackay is a frequent performer at venues and festivals across Europe (including the Aldeburgh Festival, Cheltenham Music Festival, Three Choirs Festival), America and Australia (including performances at the Sydney Opera House) and has performed with numerous orchestras including the Royal Philharmonic Orchestra, London Symphony Orchestra, Bournemouth Symphony Orchestra, BBC Symphony Orchestra, BBC Scottish Symphony Orchestra, English Chamber Orchestra, London Mozart Players, City of London Sinfonia, Royal Liverpool Philharmonic Orchestra and others.