Nicolas Andre went to the aid of the stranded 12-foot creature after it got stuck in shallow waters near Lizard Point in Cornwall.
After running to help in the rescue, he was stunned to realize it was actually a basking shark.
Mr Andre, 49, from Durham, wrapped his t-shirt around the shark's tail and pulled it to the safety of the deeper water with the aid of another man.
"I've never seen a shark that close - let alone touched one in my whole life,” Mr Andre said.
"The beach had no access, but I legged it down the hill anyway,” he added.
"I started to help the man there, and I realized that it was not a dolphin but a basking shark of about four-meters in length."