Metropolitan police praised the bravery of PC Dewayne Hamilton after he vaulted over a bridge to save a teenage girl who tried to jump on to the busy road below.
The ordeal reportedly lasted for several minutes as the pair dangled over the road waiting for help.
Eventually the London fire brigade and ambulance service were able to get a harness around the girl, and a cherry-picker crane was used to bring them back down to the ground safely.
This was an incredibly courageous act by the officer. What makes this even more impressive is that this officer only arrived at Hillingdon borough one week ago as a probationer constable. His action, which placed his own life in danger, was an extraordinary act of bravery. I would also like to pass on my sincere thanks to those members of the public who helped stop the girl falling and then stayed with her throughout the ordeal. All three emergency services worked seamlessly together and I pay tribute to the work of our colleagues in the LFB (London fire brigade) and LAS (London ambulance service)."
Hamilton said in a statement: "I am so just glad I was there and able to make difference."
"I have a child about this girl's age and all I could think about was saving her. I am so very happy we were all able to rescue her from danger."
The teenager did not suffer any serious physical injury during the rescue and police said both she and her family are now receiving support.