Polling in 2038 more votes than her closest rival, the by-election was held following the death of Councillor Tayo Oladapo who also represented Labour.
The count took place on the same day as the London Mayoral Elections where Sadiq Khan was voted as the new Mayor of London and Navin Shah retained his seat as London Assembly member for Brent and Harrow .
Carolyn Downs, constituency returning officer and chief executive at Brent council, said: “I would like to congratulate Navin Shah and Barbara Pitruzzella on their election victories and I look forward to working with them both going forward.
“I’d like to thank everyone who played their part in our democracy and turned out to vote, as well all of those from both Brent and Harrow who staffed the polling stations, counted the ballot papers and helped the election to run so smoothly.”
Mr Shah also from the Labour party polled in 79,902 votes (45%), 20,755 more than his nearest rival Joel Erne Davidson of the conservative party.
The results were announced at Alexandra Palace which hosted the north London count centre for the elections.