The speaker of the lower house announced the move Tuesday, setting the stage for a vote that could trigger a rare change in Japan's political leadership. Prime Minister Taro Aso has said he will call the national vote for Aug. 30.
The ruling Liberal Democratic Party has had a majority in the lower house for most of the past 50 years. But the main opposition, the Democratic Party of Japan, has won a series of local elections and drawn broad support in recent polls.
The party that wins a majority in the lower house picks the prime minister and government ministers from among its ranks.