Sporting a Justin Bieber Purpose hoodie, Williams replaced the chorus lyrics of his hit "Strong" with the words, "Manchester we're strong, we're strong, we're strong".
Headliner Grande was a perpetual presence throughout, performing solo hits as well as joining other artists, including hitting the stage with Black Eyed Peas for a stirring take on "Where is the Love", filling in for Fergie.
Grande and Coldplay's Chris Martin performed "Don't look back in anger", the track by Manchester Britpop band Oasis which crowds sang during vigils in the days following the bombing. "And she said that I should stop crying because Olivia wouldn't have wanted me to cry", she said.
The singer and some of her famous friends held a benefit concert in the English city to benefit the victims of a terrorist attack that took place following her performance there almost two weeks ago. "When I saw you guys all rallying together last week, it was a sight to behold".
Mumford & Sons frontman Marcus Mumford opened the show after the crowd fell silent for a minute. "We ask the strong city of Manchester and the world to join us in making the statement that hatred and fear will never win", Braun said.
Pharrell Williams told the crowd "I don't see or smell or hear any fear" at the open-air concert.More news: Officer wounded in London Bridge attack armed only with baton
"It's always felt like a home away from home to me", she said of Manchester, where she's performed multiple times.
However, just moments later, concert-goers were given an even bigger surprise when Liam Gallagher took to the stage to pay tribute to his hometown.
The crowd went wild when Justin Bieber showed up, with a guitar, to perform an acoustic version of his song "Love Yourself". I can't imagine a better, or more memorable, way to help wrap up such an inspiring evening of music and hope.
Officials say security was bolstered for the concert. "I'm really happy to come tonight, it is good for Ariana, it wasn't her fault what happened".
Grande visited young fans injured in the attack at the Royal Manchester Children's Hospital on Friday.
Seven people were killed and 48 injured in the attack.
He's 15 years old.
Proceeds from the show will go to Red Cross's Manchester Emergency Fund.