Police were called to Twickenham Road at around 6am this morning (Wednesday, April 10).
He was detained under the mental health act and has now been placed in the care of medical professionals.
If you are struggling with your mental health, the Samaritans are available to talk 24/7 on 116 123.
A spokesperson for the Metropolitan Police said: “Police were called to reports of a man attempting to self harm on a bridge on Twickenham Road, Richmond at 06:12hrs on Wednesday 10 April.
“Officers from Richmond borough attended.
“He was detained under the mental health act by officers and placed in the care of medical professionals.”