Prime minister Yusuf Gilani says the reforms represent a landmark
Pakistan's upper house has voted unanimously in favour of measures which limit key presidential powers.
The upper house vote was the final hurdle to landmark reform measures which take away the president's power to dismiss elected governments.
North West Frontier Province (NWFP) has officially been renamed Khyber Pakhtunkhwa as part of the reforms.
The legislation has sparked violent protests among a non-Pashtu speaking ethnic minority in the province.
The renaming of NWFP is intended to replace the name given under British colonial rule, but Hindko-speaking Hazaras in the NWFP object to the new name, saying it acknowledges only the Pashtun majority in the province.
At least six people have been killed in protests over the renaming in the town of Abbottabad in the province since Monday.
"Today, democracy has won," Prime Minister Yusuf Raza Gilani was quoted as saying by Reuters news agency after the vote.
"It's the first time the president, prime minister and both houses of parliament are on one page," he added.
Ninety lawmakers in the 100-member upper house - or Senate - voted unanimously in favour of the reform.
Supporters say the legislation will strengthen parliamentary democracy, weakened by periods of military rule.
Under the new measures, Pakistan's President Zardari becomes largely a titular head of state who can dismiss parliament only on the advice of the prime minister.
The prime minister is now the most powerful man in the country, with complete control of Pakistan's nuclear and conventional forces, the BBC's Syed Shoaib Hasan in Islamabad says.
The amendment has been a long-standing policy of Pakistan's political parties, but especially of the Pakistan People's Party (PPP) - previously led by Benazir Bhutto, the murdered former prime minister and wife of Mr Zardari