Grande returned to the stage in the northern city after 22 people were killed in a suicide attack at the Manchester Arena, where she was performing.
Throughout the night Grande performed her hits Be Alright and Break Free, as well as her duet Better Days with Victoria Monet.
Pharrell Williams told the crowd "I don't see or smell or hear any fear" at the open-air concert.
Katy Perry also left a mark with her resilient performance: She sang a stripped down version of her hit, "Part of You".More news: Pope pays tribute to 'martyrs' killed in Egypt attack
"So that means that we had a totally different show planned and we had a rehearsal yesterday where we changed everything and this evening has been so light and so filled with fun and love and bright energy and I want to thank you for that". "I'm not gonna let go of hope".
"Manchester, we're strong, we're strong, we're strong".
Video caption Ariana fans who were at the gig on 22 May react to One Love Manchester. And this love that you choose will give you strength and it's our greatest power ... "All we feel tonight is love, resilience, and positivity".
Before the show, Grande's manager Scooter Braun released a statement vowing that the show would go on.
"We will continue in honor of the ones we lost, their loved ones, my fans and all affected by this tragedy", she added.
Mumford & Sons frontman Marcus Mumford opened the show after the crowd fell silent for a minute.More news: Trump promises unfulfilled by House GOP health bill
Ariana Grande fans have described the nerves and excitement they felt before Sunday's huge One Love Manchester concert.
'Good even Manchester, ' singer Gary Barlow screamed. "Fear will never divide us because on this day, we stood with Manchester".
The 1990s boy band were followed by former member Robbie Williams, who performed his hit Strong with lyrics adjusted to reflect the city as well as his signature tune Angels. "We're still singing our song, our song, our song", as the crowd chanted along.
The May 22 terror attack on Manchester Arena claimed 22 lives, including seven children, and injured dozens more.
On Saturday night seven people were killed and almost 50 injured after three men drove a van into a crowd on London Bridge and set upon people in a crazed knife rampage.More news: Ariana Grande Announces Benefit Concert for Manchester Victims