The American star said her “heart, prayers and deepest condolences” were with the victims of the Manchester attack.
“I don’t want to go the rest of the year without being able to see and hold and uplift my fans,” the singer added.
Twenty-two people were killed in the explosion at the Manchester Arena.
‘Hand and heart’
The singer tweeted: “There is nothing I or anyone can do to take away the pain you are feeling or to make this better.
“However I extend my hand and heart and everything I possibly can give to you and yours, should you want or need help in any way.”
The star said: “I’ll be returning to the incredibly brave city of Manchester to spend time with my fans and to have a benefit concert in honour and raise money for the victims and their families.”
She continued: “Our response to this violence must be to come closer together, to help each other, to love more, to sing louder and to live more kindly and generously than we did before.”
‘We will continue’
The singer said she wanted the current tour to be “a safe space” for her fans to “express themselves”.
“This will not change that,” she added.
“We will continue in honour of the ones we lost, their loved ones, my fans and all affected by this tragedy.
“They will be on my mind and in my heart everyday and I will think of them with everything I do for the rest of my life.”
The star said she would reveal further details once the gig had been confirmed.