More than 50,000 crowded into Emirates Old Trafford Cricket Ground to watch Grande headline the benefit.
Take That, who are from Manchester, followed Mumford.
Grande later joined a choir from Parrs Wood High School on stage, who sang their own version of her song, My Everything, before she welcomed her boyfriend Mac Miller on to the stage saying: "Tonight is all about love, am I right?" "And I want to thank you for that".
"You guys make everyone who comes from out of town feel so welcome and we really appreciate that so when I see you guys all rallying together last week it was a sight to behold and it was incredible".
Georgia Thompson, 14, from South Shields, is one of many Ariana Grande fans caught up in the Manchester bombing who have returned to the city tonight for the special One Love Manchester benefit concert.
"Obviously I'm a little bit nervous and Laura got quite upset about it (the London attack) when she saw the news", said Mr Anderson. "I've played here a bunch of times, I've always loved Manchester - not just today, it's always felt like a home away from home for me". As a result, all proceeds from the show will benefit the We Love Manchester Emergency Fund, which was founded by the Manchester City Council, in conjunction with the British Red Cross.
Grande also showed off her close friendship with Miley Cyrus as they sang "Don't Dream It's Over". The leader of rock band Mumford & Sons then sang Timshel while strumming his guitar.More news: Katy Perry tells One Love Manchester 'love conquers hate'
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Still recovering from injuries suffered in the blast on Monday, May 22, the pair plan to meet Ariana Grande again - having met her only days ago ahead of the suicide bombing at the Manchester Arena which killed 22 people.
"As much as Ariana wants to perform the track, it will be hard for her to keep her emotions in check".
Grande came back onstage to sing Fergie's verse on the Black Eyed Peas hit, Where Is the Love? along with the group.
Others set to perform Sunday include Justin Bieber, Coldplay, Katy Perry and Usher.
Event commander Chief Superintendent Stuart Ellison said the day passed without cause for concern, with just one man arrested on suspicion of being drunk and disorderly.
The fan added during the broadcast that she cried while "driving past the arena".
She also paid tribute to 15-year-old fan Olivia Campbell who lost her life in the attack, and she recounted a conversation she had with the girl's mother.
"Finally, our thoughts remain with all those affected by the heartbreaking events of Monday May 22".