Jean-Baptiste Loeillet of London (November 18, 1680 – July 19, 1730), was a Flemish baroque composer as well as a performer on the recorder, flute, oboe, and harpsichord. He is called the London Loeillet to distinguish him from another famous composer, his first cousin Jean Baptiste Loeillet of Ghent, and he was the elder brother of Jacques Loeillet, also a composer.

Loeillet was born at Ghent, then in the Spanish Netherlands. In 1705, after his studies in Ghent and Paris, he moved to London and became known as John. In London, his last name was sometimes rendered as 'Lully' or 'Lullie': he was unrelated to Jean-Baptiste Lully, the French composer. His works were published by Walsh in London under the name of John Loeillet.

He was successful as a player and teacher of the harpsichord. He played woodwind in the Queen's Theatre in the Haymarket[1] and held musical gatherings every week at his home. His performances were well received in London; and he was responsible for introducing Arcangelo Corelli's 12 concerti grossi to Londoners. According to the New Penguin Dictionary of Music, he helped to popularise the transverse flute (a new instrument compared to the recorder) in England. He died in London.

Leopold Godowsky's piano suite Renaissance features an arrangement of one of the composer's Gigues.