The football star and his partner, Georgina Rodriguez, announced the death of their son at birth on 18 April. His twin sister, whose name has not been revealed, survived.
Ronaldo, 37, posted the black and white picture of himself smiling as he looked at and held his new daughter close to his chest.
The baby is seen wearing a knitted hat and a nappy as she lays in her father’s arm and on top of a blanket.
The Manchester United forward wrote in the caption: “Forever Love.”
Fans and fellow sportsmen, including England footballer Marcus Rashford, left dozens of red heart emojis in the comments to express their love and support for the family.
Ronaldo and Rodriguez announced they were expecting twins last October. At the time, Ronaldo shared a post featuring himself and Rodriguez holding up a sonogram picture.
He wrote: “Delighted to announce we are expecting twins. Our hearts are full of love – we can’t wait to meet you.”
The footballer is also a father to four older children, 11-year-old Cristiano Ronaldo Jr, five-year-old twins Eva and Matteo, and Alana Martina, also five.
Cristiano Ronaldo Jr, Eva and Matteo were born via surrogate mothers.
Announcing the birth of their new baby daughter and the death of their son, the couple said in a statement: “It is with our deepest sadness we have to announce that our baby boy has passed away.
“It is the greatest pain that any parents can feel. Only the birth of our baby girl gives us the strength to live this moment with some hope and happiness.
“Baby boy, you are our angel. We will always love you.”