Michael Healey said granddaughter Sorrell Leczkowski, from Adel, Leeds, was "our rock" as he paid tribute to the "clever, talented, creative girl".
In a statement issued through Greater Manchester Police, he said his wife Pauline remains in intensive care and Sorrell's mother Samantha is recovering from surgery "as she tries to make sense of the devastating loss of her daughter".
Mr Healey said: "I am absolutely heartbroken to confirm that my granddaughter was killed in the terror attack that claimed so many innocent lives.
"Sorrell was only 14, but she was our rock, she kept us all grounded. She was such a clever, talented, creative girl, there was nothing she couldn't do.
"She was going to be an architect and wanted to go to Columbia University in New York to study so that she could build hotels with slides coming out of the rooms and so that she could build her mum a house.
"My wife is currently in intensive care, and Samantha is recovering from surgery as she tries to make sense of the devastating loss of her daughter."
Mr Healey requested that the family is allowed to grieve in privacy.