Sony Music Entertainment already owned the licensing rights to the recordings from 1971 to 1975 and has now acquired the rest of the collection.
It includes hits from such artists as Teddy Pendergrass, Patti LaBelle, the O'Jays and Lou Rawls.
Kenny Gamble and Leon Huff's Grammy-winning work came to be known as "The Sound of Philadelphia".
Their recording studio on Broad Street was damaged in a fire, and will soon be torn down for a hotel and condo complex.
