Thousands of people lined the streets of Blackhall, County Durham, ahead of the service at St Joseph’s Catholic Church, where the youngster was baptised six years ago.
A piper lead the horse-drawn carriage carrying his coffin through the village, which came to a halt to pay tribute to the little boy with the beaming smile.
Some released balloons as the cortege passed and a spontaneous round of applause broke out.
Mourners dressed in superhero costumes followed the funeral procession.
Defoe, now signed for Bournemouth, left training in Spain to attend.
Former Sunderland FC manager David Moyes was also among the congregation.
Defoe struck up a remarkable friendship with Bradley after the little boy appeared as a mascot for his beloved Sunderland.
Bradley died a week ago in his parents’ arms at home following a battle with the rare childhood cancer neuroblastoma.