Snoop Dogg, Lil Wayne, Cassie, Nas and Penelope Cruz have all worked for Diddy's fashion line in the past.
The singer's print campaign, which features him stood outside a modern home in Hollywood Hills, will launch in the autumn.
Speaking about the deal, he said: "Nelly has the attitude, the swagger, and most of all the physique that our customers can both aspire and relate to.
"And let's be honest, all of the ladies out there are going to be thanking us for this campaign!"
Nelly said it was an "honour" to work for Diddy, saying he has been a fan of the entrepreneur's clothing line "for years".
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