Police were called to an incident involving a man and a woman on Kingston Bridge at approximately 10.30pm on Friday.
According to the police, an allegation of theft was made and as officers arrested the man, aged in his 20s, he entered the water.
He was not in handcuffs when he entered the water and was retrieved by emergency services at around 12.30am.
Paramedics tried to resusicitate him but he was pronounced dead. His family has been informed.
The Met’s Directorate of Professional Standards have made a referral to the Independent Office for Police Conduct which is now conducting an investigation.
Deputy assistant commissioner Laurence Taylor said: “My thoughts, and those of the Metropolitan Police Service, are with the friends and family of the man who has sadly lost his life following this incident.
“I fully appreciate the public will be very concerned. We of course share that concern.
“The Met’s Directorate of Professional Standards made an immediate referral to the Independent Office for Police Conduct as is protocol in any incident in which a person comes to harm following police contact.
“We will fully support the IOPC’s investigation.”
