The amendment proposed by the Democrat Party on a two-ballot voting system pulled through with 552 yes votes, 24 nays and 130 abstentions.
Voting on the 13 Constitution amendment bills took more than six hours and 12 were rejected because they did not meet the vote count required.
The rejected drafts included opposition Pheu Thai Party’s proposal that senators’ right to select a prime minister be taken away and ruling Palang Pracharth Party’s proposal on fighting corruption.
The Democrat Party, meanwhile, proposed amendments to Articles 83 and 91 of the Constitution.
Article 83 will be amended to revive the two-ballot voting system in which the House of Representative’s 500 MPs will comprise 400 elected from constituencies and 100 from the party-list system. The Lower House currently comprises 350 constituency MPs and 150 from party lists.
Article 91, meanwhile, deals with the calculation of party-list MPs, which will be changed in line with the two-ballot system.
However, some MPs and senators do not agree with the two-ballot system because they believe it will only benefit large political parties.
After voting was completed a panel for considering charter amendment drafts was established. The 45-member committee includes 17 representatives of the government coalition and 13 members of the opposition. The panel will spend 15 days studying the amendment draft and will hold its first meeting on June 29.