Leonhardt performed and conducted a variety of solo, chamber, orchestral, operatic, and choral music from the Renaissance, Baroque and Classical periods.

The many composers whose music he recorded as a harpsichordist, organist, clavichordist, fortepianist, chamber musician or conductor included Johann Sebastian Bach, Carl Philipp Emanuel Bach, Wilhelm Friedemann Bach, Heinrich Biber, John Blow, Georg Böhm, William Byrd, André Campra, François Couperin, Louis Couperin, John Dowland, Jacques Duphly, Antoine Forqueray, Girolamo Frescobaldi, Johann Jakob Froberger, Orlando Gibbons, André Grétry, George Frideric Handel, Jacques-Martin Hotteterre, Jean-Baptiste Lully, Claudio Monteverdi, Wolfgang Amadeus Mozart, Georg Muffat, Johann Pachelbel, Henry Purcell, Jean-Philippe Rameau, Christian Ritter, Johann Rosenmüller, Domenico Scarlatti, Agostino Steffani, Jan Pieterszoon Sweelinck, Georg Philipp Telemann, Francisco Valls, Antonio Vivaldi, and Matthias Weckmann.

In addition, Leonhardt recorded Bach's St Matthew Passion, Mass in B minor, Magnificat, and the complete secular cantatas, as well as the harpsichord concertos, Brandenburg Concertos, and most of his chamber and keyboard music; he recorded Bach's Goldberg Variations (three times), Partitas (twice), The Art of Fugue (twice), The Well-Tempered Clavier, French Suites, English Suites (twice), Inventions and Sinfonias, and many other individual works for the harpsichord, clavichord, or organ.

More generally, Leonhardt significantly influenced the technique and style of many harpsichordists through his teaching, editions, and recordings; his students and collaborators included harpsichordists and keyboard players such as Robert Hill, Bob van Asperen, John Butt,[3] Lucy Carolan, Lisa Crawford, Alan Curtis, Menno van Delft, Richard Egarr, John Fesperman, John Gibbons, Pierre Hantaï, Frederick Renz, Elaine Thornburgh, Ketil Haugsand, Siebe Henstra, Philippe Herreweghe, Christopher Hogwood, Ton Koopman, Karyl Louwenaar,[4] Charlotte Mattax,[5] Davitt Moroney, Jacques Ogg, Martin Pearlman (music director of Boston Baroque), Edward Parmentier, Christophe Rousset, Louise Spizizen, Andreas Staier, Skip Sempé, Domenico Morgante, Peter Waldner, Francesco Cera, Jeannette Sorrell (music director of Apollo's Fire, The Cleveland Baroque Orchestra), Colin Tilney, Glen Wilson,[6] and Chris Mary Francine Whittle.

In comparing recordings of Bach's Goldberg Variations, Butt asserts that a "classic case" of the anxiety of influence is at work in the Goldberg recording by Ton Koopman, in which "what is immediately evident is the incessant ornamentation added to virtually every measure, often regardless of whether there is already obvious ornamentation in the notation.... my immediate reaction is often that this performance's principal message is 'Not Leonhardt'.

Among the awards given to him were the Medal of Honour for the Arts and Sciences from the Netherlands, presented to him by Queen Beatrix in 2009, and the 1980 Erasmus Prize, which he shared with Nicolaus Harnoncourt; it honored their recording of the complete Bach cantatas.

(Leonhardt donated the money he received from the Erasmus Prize to Oudezijds 100,[8] an ecumenical Christian charity operating "in the red-light district [of] Amsterdam" that "addresses the issues of drug-addicts, prostitutes, refugees, and the homeless.").