The Tower lifeboat team was passing under Cannon Street railway bridge at around 6pm on April 11 when they spotted people on the river bank shouting and pointing at something in the middle of the Thames.
RNLI helmsman Steve King said: "We spotted a man in the water who seemed to be struggling. It appeared that cold water shock had disabled his ability to swim and he was going under the water. We made our way to the man’s position and the crew managed to grab hold of him just before he went under the surface.
"The man was conscious and breathing as we got him on board. If we hadn’t got to him when we did we think he would have drowned. I’d like to thank all those people on the river bank who spotted the man in difficulty and helped us save his life."