Before her performance, she and her dancers held hands in solidarity.
In between renditions of Giants and Rule The World, Gary Barlow told the crowd: "Thank you everybody for coming out tonight, thank you for everybody watching at home, thanks to Ariana for inviting us tonight".
Her boyfriend Mac Miller also joined her on stage for a surprise performance of "Dang!"
Repeatedly telling fans "I love you, I love you", Ariana wiped tears from her eyes as she gave her final performance of the night.
"So that being said, we had a totally different show planned and we had a rehearsal yesterday and we changed everything".
Cyrus said she was "so honored to be at this incredible event" and performed "Happy" alongside Pharrell, who also sang "Get Lucky". "Look in their eyes and tell them you love love", Perry instructed everyone.
"I love you Manchester", she yelled to the crowd. It's a place we all love.
Ariana Grande made an emotional return to the stage at a tribute concert to the victims of the Manchester terror attack. On Saturday, she had visited fans still receiving hospital treatment for injuries sustained during the Manchester attack. "Somewhere Over The Rainbow", originally written for 1939 The Wizard Of Oz film, was the most ideal peaceful lullaby to close the show after so many spectacular performances from Miley Cyrus, Katy Perry, and many more.More news: Michael Bloomberg offers to foot US cost of Paris Agreement
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"I don't feel or smell or hear or see any fear in this building", Williams said. "All we feel tonight is love, resilience, and positivity".
The leader of rock band Mumford & Sons sang "Timshel" while strumming his guitar at the "One Love Manchester" concert, held at the city's Old Trafford cricket ground.
Gallagher and Take That hail from Manchester.
Robbie Williams led the thousands inside the venue in a chorus of: "Manchester, we're strong, we're strong, we're strong".
Williams serenaded the crowd with his song Strong, changing the words to, "Manchester we're strong". Twenty-two people were killed and more than 100 wounded when Salman Abedi detonated an explosive device in the Arena foyer as fans were departing.
The concert comes the day after attackers targeted the heart of London, using a van to mow down pedestrians on London Bridge before launching a stabbing frenzy at Borough Market. Proceeds from the event are going to the We Love Manchester Emergency Fund.
Mesfin Fekadu reported from NY.