Gallagher also performed the band's Rock "n" Roll Star and his own single, Wall Of Glass, before telling the 50,000-strong crowd at the Old Trafford cricket ground that Live Forever was for "the attractive people killed and injured in the Manchester terror attack".
Wearing a sweat shirt graffitied with the legend One Love Manchester, Grande showed up several times throughout the show alongside Coldplay, Black Eyed Peas and Little Mix to celebrate the fighting spirit of Manchester.
"The only thing we'll feel here tonight is love, and positivity".
All proceeds from the event will go toward the "We Love Manchester Emergency Fund", in partnership with the British Red Cross and Manchester City Council.
Sunday's concert was held on the eve of the first funeral of Manchester attack victims.
Grande's management answered doubts on Twitter, just hours before the concert.
The crowd help up one finger for one love during the Black Eyed Peas' performances.
"Thank you Ariana so much for your incredible courage and your strength and for inviting me to participate in this evening".
Justin Bieber paid an emotional tribute to all the victims killed in the horrific attack.
Rather than wait till the end of the show to perform, Grande appeared at various points to do her songs (including "Be Alright" and a throbbing "Break Free") and to collaborate with other artists on the bill.
U.K. TV giant ITV had moved the season finale of its hit competition show Britain's Got Talent from that night to Saturday.
Dragging fellow singer Katy Perry into the mix - after she praised Queen Elizabeth II for visiting the injured who are recovering in a number of hospitals in Manchester - Piers said it "might have been nice" if Ariana had stayed in the United Kingdom and done the same. "And she would have wanted to hear the hits".
"That's what I hope everybody can take away", Selena said of the concert's important theme.
The attack left a gruesome scene, injuring more than 20 dead an roughly 50 more injured at a concert predominantly attended by young girls and their parents.
While Justin Bieber was giving his emotional final remarks, which reduced him to tears, the live broadcast camera panned to the audience where one special group stood out.
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