Nationalist former Tokyo governor Shintaro Ishihara, whose bid to buy the islands at the centre of the dispute with Beijing sparked months of tensions, secured a parliamentary seat as leader of Japan's third-largest party.
His rabble-rousing Japan Restoration Party won between 46 and 61 seats, NHK said, giving him weight enough to shout from the parliamentary sidelines.
Public unease about a worsening security environment - after North Korea fired a rocket over Japan's southern islands last week and China sent a plane into Japanese airspace - bolstered Ishihara in the vote.
The Japan Restoration Party - also led by Osaka Mayor Toru Hashimoto, who is another polarising figure - could become a future coalition partner for Japan's Liberal Democratic Party, analysts said. Ishihara's party wants to boost defence spending and maritime surveillance in response to the territorial row with China. But it has flip-flopped on the issue of nuclear power. Voters elected the political heir of Ishihara, rejecting a candidate strongly endorsed by anti-nuclear activists. Naoki Inose, a prize-winning author and former deputy to Ishihara, won an easy win against eight opponents, including Kenji Utsunomiya, a veteran human rights lawyer and Japan Federation of Bar Associations ex-president.
Utsunomiya was endorsed by left-leaning parties because of his calls to permanently to close Japan's nuclear plants following the atomic catastrophe at the Fukushima Daiichi power plant after last year's tsunami.
The vote was essentially a referendum on Ishihara, who was a year into his fourth four-year term as governor when he abruptly resigned to lead the new party. Inose has pledged to back Ishihara's bid for Tokyo to host the 2020 Olympic Games despite the city's costly failure to win the 2016 Games.
Additional reporting by Reuters