Life keeps interrupting the serious business of genealogy, so here is a first effort at transcribing and translating.
Mar(riage) Jean Baptiste Desmarets and Miss Marie Louise Adam step(?) Leonard
Today (the) ninth day of the month of September, (one) thousand seven hundred forty three, after a publishing of banns done during the Sunday parish mass, the parties having obtained dispensation from other publishings, given the authorisation of His Honour the Intendant for the celebration of the marriage, I have joined in lawful matrimony Mr Jean Baptiste Desmarets, born in the town of Salenou(?), parish (of) Our Lady Saint Mary, in …. , son of Mr Desrives(?) Desmarets, former Captain of the Brittany Dragoons, Knight of the Royal and Military Order of Saint Louis, and …. of the King, and of Lady Marguerite de Landas(?) …. and .... Paimpol(?), and Miss Marie Louise Adam, stepdaughter(?) of the late Noël Leonard the younger, daughter of the late Louis Adam and Mrs Luce Fabulet, all residents of this parish, without any opposition having been notified to us and having no knowledge of any civil or canonical impediment in good faith of which I have signed with the named(?) witnesses to this effect
Gisard, Lalung, monk, Desmarets, groom, Albay, Jean Fabulet, Puget(?)
No doubt about the bride, I think. Marie Louise Adam was the daughter of Louis Adam and his wife Luce Fabulet, who after his death had married Noël Leonard. In the text neither husband is given the honorific Mr, but that may not be significant.
What puzzles me, and you too or you would not have asked the question, is the groom. His birthplace eludes me. His father was important - a captain of dragoons and a knight of St Louis – but I cannot be sure of his first name. Nor can I trace his regiment, which must have been disbanded or renamed since then. Nor have I found him among knights of St Louis (whose sons, if the holder was a commoner, became hereditary nobles). His mother was important, being called Lady rather than Mrs, but I'm stuck on her last name and her connection to what may be the Breton town of Paimpol.
So I think I must bow out, and open the challenge to other WikiTreers.
PS By the way, his last name is written many ways and on Martinique seems to have become phonetic, but to preserve the link with metropolitan France the most authentic form is probably Desmarets.