The Democratic Party of Japan won more seats than the Liberal Democratic Party in Sunday's House of Councilors election, marking the first time the LDP was outperformed by an opposition party since 1989, final results show.

The LDP fell shy of its target of winning 51 seats, but the party's ruling alliance with New Komeito retained a solid majority in the 242-seat Upper House.

Of the 121 seats contested, the LDP won 49 against the 50 captured by the DPJ.