The concert was organised by the 23-year-old popstar after suicide bomber Salman Abedi's attack at her show less than two weeks ago.
One star who joined the American singer this evening was Justin Bieber who gave an emotional performance of Love Yourself.
But as he sang, a member of the police force stole the spotlight as he was shown on television screens across the nation dancing with a group of young girls.
The unknown officer could be seen holding hands with the youngsters in a circle for a ring of roses.
One Love Manchester: A police officer could be seen dancing with young fans
One Love Manchester: The heartwarming moment took place during Justin's set
The heartwarming moment left many of those at home in tears as they insisted that it proved to terrorists that they would never win.
Taking to social media to comment on the police man's actions, one viewer tweeted: "The police officer dancing in a circle with little kids has warmed my heart! #OneLoveManchester."
While another added: "Hey terrorists. There's a policeman doing ring a ring of roses at #OneLoveManchester. You lose. You will always lose."
"THE SECURITY WITH THOSE KIDS IM CRYING SO HARD #OneLoveManchester (sic)," a third wrote.
One Love Manchester: The police officer could be seen holding hands with the fans One Love Manchester: Crowds gather for Ariana Grande benefit gig Sun, June 4, 2017
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Crowds gather for the Ariana Grande One Love Manchester benefit gig in tribute of the Manchester terror attack victims.
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Girls wearing Ariana Grande t-shirts waiting to attend the One Love Manchester benefit concert for the victims of the Manchester Arena terror attack
One Love Manchester: Viewers were left in tears by the emotional moment
Another continued: "More should be spoken about the police man doing ring a ring posy with the kids! #OneLoveManchester #whatitsallabout."
A fifth went on to say: "Best picture of the policeman dancing with everyone. I f**king love my country #OneLoveManchester."
Viewers were also left in tears when Ariana took to the stage to join Parrs Wood High School Choir to sing her hit My Everything.
One schoolgirl was overcome with emotion and broke down in tears as the pop star wrapped her arms around her.