Giovanni Paisiello (or Paesiello; 9 May 1740 – 5 June 1816) was an Italian composer of the Classical era, and was the most popular opera composer of the late 1700s. His operatic style influenced Mozart and Rossini.

Paisiello was born in Taranto in the Apulia region and educated by the Jesuits there. He became known for his beautiful singing voice and in 1754 was sent to the Conservatorio di S. Onofrio at Naples, where he studied under Francesco Durante, and eventually became assistant master. For the theatre of the Conservatorio, which he left in 1763, he wrote some intermezzi, one of which attracted so much notice that he was invited to write two operas, La Pupilla and Il Mondo al Rovescio, for Bologna, and a third, Il Marchese di Tidipano, for Rome.

His reputation now firmly established, he settled for some years at Naples, where, despite the popularity of Niccolò Piccinni, Domenico Cimarosa and Pietro Guglielmi, of whose triumphs he was bitterly jealous, he produced a series of highly successful operas, one of which, L'idolo cinese, made a deep impression upon the Neapolitan public. The young Mozart and his father met him in Bologna in 1771.

In 1772, Paisiello began to write church music and composed a requiem for Gennara di Borbone, of the reigning dynasty. In the same year, he married Cecilia Pallini, and the marriage was a happy one. In 1776, Paisiello was invited by the empress Catherine the Great of Russia to Saint Petersburg, where he remained for eight years, producing, among other charming works, his masterpiece, Il barbiere di Siviglia, which soon attained a European reputation. The fate of this opera marks an epoch in the history of Italian art; for with it the gentle suavity cultivated by the masters of the 18th century died out to make room for the dazzling brilliance of a later period.

When, in 1816, Gioachino Rossini set another version of the libretto by Cesare Sterbini under the title of Almaviva ossia la inutil precauzione the fans of Paisiello stormed the stage. Rossini's opera, now known as Il barbiere di Siviglia, is now acknowledged as Rossini's greatest work, while Paisiello's opera is only infrequently produced—a strange instance of poetical vengeance since Paisiello himself had many years previously endeavoured to eclipse the fame of Giovanni Battista Pergolesi by resetting the libretto of his famous intermezzo, La serva padrona.

Paisiello left Russia in 1784, and, after producing Il Re Teodoro at Vienna, entered the service of Ferdinand IV of Naples, where he composed many of his best operas, including Nina and La Molinara.

The Irish tenor Michael Kelly witnessed another meeting between Paisiello and Mozart when he visited Vienna later that year. Mozart had just finished a string of piano concertos, K. 449 and 453, written for his pupil Barbara Ployer. When Ployer’s father arranged a performance at his summer estate in Döbling, Mozart wrote to his father, "Fräulein Babette will play her new concerto in G and I shall play the Quintet and then we’ll perform together the grand sonata for two pianos. I shall fetch Paisiello with my carriage for I want him to hear my compositions as well as my pupil."

After many vicissitudes, resulting from political and dynastic changes, he was invited to Paris (1802) by Napoleon, whose favour he had won five years previously by composing a march for the funeral of General Hoche. Napoleon treated him munificently, while cruelly neglecting two more famous composers, Luigi Cherubini and Étienne Méhul, to whom the new favourite transferred the hatred he had formerly borne to Cimarosa, Guglielmi and Piccinni.