Journalist Donald MacLeod was returning home to Stoke Newington, north London, after drinking two small glasses of wine with a friend in the El Vino wine bar on Fleet Street, when the accident happened in March 2010.
The 63-year-old father-of-three was in a coma for several weeks and now needs round-the-clock care.
A former editor of Education Guardian and head of communications for the Russell group of universities, he brought the claim against the Metropolitan Police through his wife Barbara, who lives in Inveresk, near Edinburgh.
Mr MacLeod, a keen and safety conscious cyclist who used his bike daily, was wearing a helmet and a high-visibility jacket with his bicycle lights illuminated, said Judge Martin McKenna, who ruled there was no question of contributory negligence.
At the point where Mr MacLeod was hit - at a mini-roundabout in Canonbury - the road had narrowed and he would have contravened the Highway Code if he had ridden on the pavement.
It was the responsibility of the police driver, who was on his way to a shooting in Hackney with three other officers, to pass Mr MacLeod safely, and the cyclist could not be criticised for failing to take measures to avoid the impact, despite the car's siren and flashing lights.
The officer, who entered the roundabout at 55mph, drove at an excessive speed in circumstances where he could not bring the car to a halt in time to avoid him.
Following the ruling on liability, the amount of damages will now be assessed if not agreed.