They included the Manchester Survivors Choir, made up of people who were at the arena on the night of the fateful concert last May 22, and Parrs Wood High School's Harmony Group, whose post-attack tribute went viral a year ago.
The American singer Grande, who visited the injured in hospital in the wake of the bombing and returned two weeks later to host a fund-raising concert, wrote on Twitter: "Thinking of you all today and every day I love you with all of me and am sending you all of the light and warmth I have to offer on this challenging day".
On May 22 a year ago, a terrorist detonated an explosive device as fans were leaving Grande's concert at the Manchester Arena, killing 22 innocent people and injuring more than 500.
Manchester Together in Albert Square featured songs by Elbow and Oasis.
Over 3,500 singers have come together to lead a chorus of amateur voices in a mass sing-along to remember the Manchester Arena attack victims.
"The last thing I would ever want is for my fans to see something like that happen and think it won", she said.
Last night's evening of solidarity through music began with a series of video messages from some famous names, including many Mancunians.More news: MI vs KXIP: Preview, head-to-head and Fantasy XI
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Grande recently opened up about the terror attack outside her concert premises, saying the memories of the incident are still fresh.
Daren Buckley, who is in Manchester Survivors' Choir, said he had found comfort in singing, but that his recovery was far from complete.
The Lord Mayor of Manchester, Joan Hitchen, thanked the emergency responders who helped "bring our Manchester together again".
On the altar stood 22 lighted candles, made from the wax of thousands of candles left at St. Ann's Square in the days after the attack.
A minute's silence - observed nationwide - was held at 2.30pm with tears inside the cathedral, where photographs of those killed were displayed on screens, and outside, where thousands watched in Cathedral Gardens.
Prince William and the Prime Minister privately met bereaved families at the cathedral following the service and both attached notes to one of the Trees of Hope, a trail of small Japanese maple trees from Victoria Station to St Ann's Square, to add to the many thousands of similar messages of support and hope left by members of the public.
Bells will ring out across the city center at 10:31 p.m.to mark the exact moment of the explosion previous year.