The 21-year-old has signed a two-year deal at Ewood Park following a successful trial with the Championship outfit.
A statement from the club read: "A powerful presence at the back and a goal threat from set plays, Songo'o has been training with Rovers since early July and impressed in the pre-season friendlies against Wrexham and Portimonense.
"The French-born centre-back hails from a famous footballing family. His dad, Jacques, is a former Cameroon international goalkeeper and his older brother, Franck, came through the ranks at Barcelona."
Songo'o's arrival is the 11th of the summer at Blackburn.