Tokyo-based Sega will offer 9.25 euros per share for Rovio, a 19% premium over Friday's closing price of 7.775 euros.
Rovio, which has been conducting a strategic review, on Saturday said it was in talks with Sega over a possible tender offer. The Wall Street Journal had reported on Friday that a deal between the two companies was imminent.
Israeli peer Playtika, had made a preliminary bid in January to buy Rovio for 683 million euros, but the Angry Birds maker confirmed last month talks had ended.