Rafinha, who was born in Sao Paulo, had been at Barcelona since 2006, when he joined its youth team. He spent the 2013-14 season on loan at Celta Vigo. After nine months out after surgery on his right knee, he made his first appearance of the season last week as a late substitute in Barcelona's Copa del Rey defeat at Espanyol.
"It's an important stage in my life," he said, "and I had a lot of desire to approach this new phase in my career." Inter has slipped to fourth in Serie A, 11 points behind leader Napoli. It could slip out of the Champions League places if Roma wins its match in hand on Wednesday.
"I hope to play in as many matches as possible and help the team to reach our objective which is Champions League qualification," Rafinha said.