During his time at Sunderland, the England striker struck up a close friendship with Bradley, who died last week from neuroblastoma.
The funeral will take place at St Joseph's Church in Blackhall, with the memorial service also set to be played on loud speakers outside.
The family will then be having a private ceremony at a crematorium.
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Bournemouth posted a message on the club's official Twitter feed which said: "@IAmJermainDefoe has today departed our pre-season training camp and returned to the UK for the funeral of Bradley Lowery."
Today, a message was posted on Bradley Lowery's Fight Against Neuroblastoma Facebook page to ask those attending the funeral not to ask for autographs.
It said: "Can I ask people not to approach anyone tomorrow for autographs or photos. Everyone is at the funeral to pay their respects and say goodbye."
Defoe, 34, signed a three-year deal with the Cherries after leaving Sunderland following their relegation from the Premier League.
Eddie Howe's squad are currently away in Marbella, where they will take on Portuguese side Estoril in a friendly on Saturday.
Bournemouth open the new Premier League season at West Brom on August 12.