Jean-Baptiste Loeillet of London (18 November 1680 – 19 July 1730), also known as John Loeillet, 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 De Gant, 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.