Lawyer Virginia Raggi of the anti-establishment Five Star Movement has made history as the first female mayor of Rome.
The 37-year-old lawyer won 67 percent of the vote in Sunday's run-off ballot.
The party also won in Turin, a center-left stronghold. The victories could be a springboard to winning in national elections due to take place in 2018.
It marks a bitter blow for the Italian prime minister, Matteo Renzi, and his Democratic Party.
"A new era is beginning with us," said Raggi, who won in the run-off ballot. "We'll work to bring back legality and transparency to the city's institutions."