Folajimi “Jimi” Olubunmi-Adewole, 20, was on his way home from work at a central London restaurant when he and another man, Joaquin Garcia, entering the water at around midnight on Saturday April 24.
The Coastguard and the Metropolitan Police Marine Policing Unit rescued the woman and Joaquin, but could not locate Jimi.
Joaquin, 21, told of how he and Jimi counted down before they both plunged 10ft into the icy water.
The Argentinian-born chef and the woman were saved, but sadly Jimi was swept to his death.
He explained how he swam to the woman, and helped keep her afloat until the police arrived at around 12.30am on Saturday.
An inquest heard that an eyewitness saw the two men jump into the river near London Bridge in an attempt to save a woman, who could be heard shouting: “Help me, help me, I can’t swim.”
The witness recalled seeing the pair run down steps to the river bank before partially undressing and jumping in.
Police arrived shortly afterwards and rescued Mr Garcia man and the woman, but Jimi was found dead almost six hours later, the court heard.