Off-duty PC Corin Evans sprung into action after the woman was hit by the vehicle in Mandeville Road on February 11 last year.
Police said the woman, called Tania, was crossing the road and hit her head on the windscreen with such force the glass shattered.
She was thrown into the air before falling to the ground.
PC Evans, an emergency response officer based in Harrow, began chest compressions and told a member of the public to call an ambulance.
He said: "My initial reaction was shock, but I knew I had to get to her as soon as I could because the impact was so significant - it was clear she was going to be extremely hurt.
"I did the initial checks we’re taught in our emergency life-saving training (ELS) and after no response I checked her breathing.
"It was clear there was nothing and I couldn’t feel a pulse. I could also see a pool of blood starting to appear from behind her head.
"I knew then that with blood in her lungs, CPR wouldn’t be effective.
"I asked another member of the public to hold her head, slightly tilt it to the side to try and drain the blood from her mouth whilst I continued giving chest compressions."
London Ambulance Service (LAS) paramedic Chris Richardson said by this stage, the patient was breathing and had a faint pulse.
PC Evans added: "When we arrived at the hospital, the medical team told me her chances of survival were very slim due to the nature of her injuries.
"I was told to expect her to die.
"I was in shock mainly. But once she came out, she was in a coma and was being monitored.
"At that point it was more relief, relief that she had a chance of surviving.
"I was told she would very possibly have lasting brain damage, however thankfully that turned out not to be the case and she made a full recovery."
PC Evans was presented with a London Ambulance Service (LAS) Chief Executive's Commendation at the annual LAS VIP awards.
Following her recovery, Tania was reunited with PC Evans when he was presented with a Borough Commander's Commendation in March.
She said: "What else can I say, when thank you is never going to be enough."
Following the collision Shamil Shah, 27, Woodhall Avenue, Pinner, pleaded guilty to careless driving, possession of Class A drugs and failing to notify of a disability on August 4 last year.
He was given six points on his licence, fined £180 and ordered to pay £85 in court costs and £30 in victim service costs.
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