Steve Chamberlain, who works on Wightlink St Clare, was working with colleagues alongside Camber Dock, in Portsmouth, when someone shouted ‘man overboard’.
The crew spotted the man in the water, around 11pm last night, and tried to throw a life ring to him.
But after a few failed attempts, Steve, from Hilsea, took off his coat and plunged into the freezing waters.
The 46-year-old said: ‘I just acted instinctively when we saw the man wasn’t able to get into the life ring.
‘We carry out emergency drills all the time but it’s different when it’s happening for real.
‘Getting the man to safety was team work and I’m grateful to my fellow crew members for their support.’
The two men were helped out of the water by Steve’s fellow crew members Paul Cooke, Robbie Mihell and Chris Fremantle. They were taken onto the pontoon, in Broad Street, where paramedics were waiting.
Both Steve and the man were taken to hospital for hypothermia.
Wightlink operations director Daryl Palmer said: ‘We are very proud of Steve and his colleagues for acting so promptly.
‘It was a cold winter’s night and I’m sure the man would have died from hypothermia if he had not been spotted by the crew and rescued by Steve.’