The French goalkeeper has signed a three-year-deal with the Sea Robbers.
Delle has played for FC Metz, OGC Nice, Cercle Brugge, Racing Club de Lens and made two appearances for Feyenoord in the Eredivisie last season.
Pirates released Jackson Mabokgwane last week and have Brilliant Khuzwayo, Siyabonga Mpontshane and Wayne Sandilands in their goalkeeping department.
The Buccaneers had four goalkeepers last season and have brought in Delle to replace Mabokgwane.
“I am glad to join this prestigious football club called Orlando Pirates and starting a new adventure in South Africa,” Delle told Pirates’ website.
“Happy to be part of an ambitious club with amazing fans who will accompany us on the road of success. I think that I will be the first French player to play for the Pirates, I would like also be the first to win titles there. Let’s go for it, it starts by a good pre-season!”