Andy Peckett, 30, flew into action when he saw his fellow parachutist, Maurizio Bram billa, hurtling towards the earth unconscious after hitting his head on the aircraft tailgate as he jumped from a Hercules at 15,000ft.
As the Italian cartwheeled out of control, Mr Peckett dived out to reach him and open his parachute.
Mr Brambilla was only 10 seconds from the ground, at 4,000ft, when Mr Peckett, a former member of the Royal Marines Free Fall team, caught up with him. He opened the unconscious man's parachute, then his own, and both men landed safely. Mr Brambilla needed six stitches in a head wound.
The incident happened last August when the two men were among a team of 24 skydivers attempting a formation drop in the Espace Skydiving Boogie Festival at Vichy, near Paris.
Mr Peckett, a company director, of Purton, Swindon, Wiltshire, received the Royal Humane Society bronze medal.