The Frenchman scored eight goals for Parma last season and joins just two days after Antonio Cassano made the move in the opposite direction.
"Ishak Belfodil is an Inter player," a statement read on the club's website. "The Algerian striker, a naturalised Frenchman, has been signed from Parma in a co-ownership agreement.
"He has signed a five-year contract which ties him to Inter until 2018."
Belfodil was on loan at Bologna in 2012, but did not score a goal for the club.