According to preliminary results, he has won by a comfortable margin over conservative rival Rachida Dati, who admits defeat.
Grégoire describes the win as a victory for “a vibrant Paris, a progressive Paris.”
In France's second-largest city, left-wing mayor Benoit Payan has retained his post with a victory over far-right candidate Franck Allisio, according to preliminary results.
With just over a year left until the next presidential election, the French municipal elections have been seen as an important gauge of which political camp has the upper hand.
