It has been a very difficult task for historians to sift through the various Jean Baptiste Loeillets that music history has to offer; there were at least four late seventeenth- and early eighteenth-century composers who either were christened with some form of the name, or whose music is to be found published under the name. Jean Baptiste Loeillet de Gant, born in Ghent, in July 1688, was the cousin of the eight-years-older composer known simply as Jean Baptiste Loeillet (who, happily enough for musicologists, moved to London and informally changed his name to John, thus simplifying identification a bit); as composers, the two were frequently mistaken for one another during their lifetimes, and so today we cannot be altogether sure which of them composed which pieces -- it is, unfortunately, likely that publishers issued music by both under the name "Jean Baptiste Loeillet de Gant" -- but it seems safe to say that of the two, the one born in 1688 (the "proper" Jean Baptiste Loeillet de Gant) was the less prolific and in a certain sense the less significant composer.
Loeillet de Gant (or de Gand) was born into a long-established family of Flemish musicians: he was the son of a Pierre Loeillet, who was in turn fathered by Jean Baptiste Francois Loeillet, who was not actually a professional musician but whose brother was. Not much is known for certain about the life and career of De Gant. He grew up in Ghent but at some point moved to France to serve the Archbishop of Lyons there, and probably died in the early 1720s.
Loeillet de Gant can be summed up fairly easily as a composer: he took the reigning Italianate style of chamber music, added a healthy dose of French ornaments to it, and then did his best to develop himself into a fine craftsman. His catalog is not weighty -- a few dozen sonatas and trio sonatas for winds or violin and basso continuo, and some sonatas (duets) for two flutes unaccompanied -- but he imbued the music he wrote with a depth of contrapuntal interest, a relative balance of importance between all the voices and parts, that is relatively unusual for music of his day and that makes it valuable in spite of its bulk (or lack thereof).