Wiltshire Fire & Rescue Service was called to the Kennet and Avon Canal at Moulton Drive, Bradford on Avon at 3.33am after a passer-by saw a canal boat well alight.
The cause of the fire is under investigation, but it is believed to have started accidentally.
The identity of the man will be released by Wiltshire Police once next of kin have been informed.
Crews from Bradford on Avon, two from Trowbridge and Melksham attended, together with the heavy rescue unit from Trowbridge.
Four breathing apparatus wearers used two hose reel jets and a main jet to tackle the blaze.
Wiltshire Police sealed off the road at Moulton Drive and the footpath alongside the Kennet and Avon Canal at Bradford on Avon.
Because of the damage to the boat, and the difficulty in getting safe access on board, firefighters remained on scene for some 12 hours, with a relief crew being mobilised from Corsham.
Wiltshire Fire & Rescue Service offers free safety checks to anyone living or working on a canal boat. To request a visit, or for more information about keeping safe, visit www.wiltsfire.gov.uk/boatsafety