In March 1805, Magon commanded a division at Rochefort that included the ships of the line "Algésiras" and "Achille". He joined Villeneuve in the Antilles and commanded the rearguard in the Battle of Cape Finisterre (July 1805) against admiral Robert Calder's squadron. At Trafalgar the following October (Magon's twelfth battle, aged only 42), Magon was still on the "Algésiras" as part of the Spanish admiral Gravina's light squadron, which was attacked by Collingwood's squadron. The crew of the "Algésiras" was about to board the "Tonnant" when the "Colossus" and "Bellerophon" came to their admiral's aid. Magon was wounded by musket balls twice but remained at his post and led the fighting for five hours before finally being killed by a third such ball just before his vessel was itself boarded and captured.