Lesley studied at the University of York and then as a postgraduate at the Royal Academy of Music. She was appointed principal clarinet with Sir Roger Norrington's London Classical Players, Sir John Eliot Gardiner's English Baroque Soloists and Orchestre Révolutionnaire et Romantique. She has toured many times in Europe, the United States, and Japan, including performances with Stockhausen's chamber ensemble and with the Academy of Ancient Music. She teaches at the University of York, and formerly taught at the Royal Northern College of Music, by which she was conferred Honorary Membership in 2021. She has an honorary doctorate from the University of York.