"The agreement includes an eight-million-euro ($9 million) purchase option," the club said.
The arrival of Boateng, 31, will provide much-needed cover for Luis Suarez up front in Ernesto Valverde's squad following the departure of Munir El Haddadi to Sevilla.
The fiery forward has been a successful stopgap many times before, which Barca boss Ernesto Valverde valued in his decision to bring him in.
"He doesn't seem to need much time to adapt, he knows his stuff and can start playing straight away," Valverde.
"He's comfortable in many positions, as a central striker or playing off another striker, and even deeper too," Valverde told the club website.