The Sweden international, who was a reported target for Liverpool due to being out of contract at the end of the season with the Dutch club, had found it difficult to nail down a first-team spot under Philip Cocu but now bolsters the attacking threat of the Ligue 1 outfit.
"He is a very technical player who impressed me when I came up against him in a friendly match when I was at Valenciennes," Rennes coach Philippe Montanier said at a press conference. "I remember that he played his part in the beating that we took in that game.
"He is not going to change everything on his own but he will give us something extra. It doesn't matter if he is big, small, blond. The objective is to have a talented and valuable player. He has always played as a striker, even if he has dropped a little deeper in Eindhoven, where they have a little phenomenon in that position (Memphis Depay). That proves his versatility."
Toivonen has signed a three-and-a-half-year contract with Rennes.