The controversial bill, proposed by the right-wing government of Prime Minister Shinzo Abe was approved by the Senate on Friday, a few days after it was passed in the lower house.
The Senate vote in favour was expected as the coalition government led by Abe's Liberal Democratic Party (LDP) holds a majority of seats there.
The opposition raised motions to stop the law but each move was rejected by the PLD members and their allies. The law allows government ministers to designate as a state secret information related to defence, diplomacy, counter-intelligence and counter-terrorism.