"It's great to be back and I'm really looking forward to this challenge," Defoe said in a statement.
"The Bournemouth fans know that every time I pull the shirt on I will give 100 percent, and the one thing I can guarantee is goals."
However, the 34-year-old England international's 15 goals in 37 league appearances last season were not enough to keep Sunderland in the Premier League.
His Sunderland form earned him an England recall under manager Gareth Southgate and he scored on his return against Lithuania in a World Cup qualifier in March.
Eddie Howe's Bournemouth, who finished ninth last season, begin their new campaign at West Bromwich Albion on Aug. 12.
(Reporting by Hardik Vyas in Bengaluru; Editing by Alison Williams)
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