Santorum appeared in Gettysburg, PA together with his family to announce the decision. He said the Good Friday weekend had been a time of prayer and soul searching for he and his wife, as their daughter Bella became ill and was in hospital. He said they had to make the right decision as parents.
He gave the address in his home state of Pennsylvania, two weeks before the Republican presidential primary there.
Santorum faced a tough fight in his home state against Romney.