In 1952 he became professor of harpischord at the Vienna Hochschule fur Musik. He met Nikolaus Harnoncourt who had similar interests to his. He soon became professor of harpsichord at the Amsterdam Conservatorium and remained there until 1988. He was also organist at the Waalse Kerk, Amsterdam. This church has a very famous historical organ. He became well known for his harpsichord concerts and recordings. He led the Leonhardt Baroque Ensemble with the English counter-tenor Alfred Deller with whom he made one of the first recordings of some Bach cantatas. The ensemble included his wife Marie, as well as Nikolaus Harnoncourt who played the cello. Together with Harnoncourt he conducted and recorded all Bach's cantatas.