Pro-Zardari lawmakers, some in tears, shouted "Long live Bhutto!" as the figures came in. The couple's two jubilant but tearful daughters, one carrying a portrait of their late mother, smiled and hugged friends in the gallery of the National Assembly.
But Saturday also brought a brutal reminder of the threats to the nuclear-armed nation's stability, when a suicide car bomber killed at least 17 people and wounded 80 near the northwestern city of Peshawar.
The blast destroyed a police checkpoint, collapsed several shops nearby and left a three-foot crater in the road. Civilians dug frantically with their hands in hopes of finding survivors.
Already head of the main ruling party, Zardari becomes one of the most powerful civilian leaders in Pakistan's turbulent 61-year history. Last month, he marshaled a coalition that forced longtime U.S. ally Musharraf to quit as head of state.
Zardari, a novice leader untested on the international stage and stained by past corruption allegations, takes over at a critical time for the volatile, nuclear-armed Muslim nation of more than 160 million.
Pakistan's economy is crumbling, and Saturday's attack was the latest in a string of suicide bombings usually claimed by Islamic militants who have steadily gained strength since Pakistan joined the U.S. war on terrorism in 2001.
Washington is pressing Pakistan hard to eradicate Taliban and al-Qaida havens near its border with Afghanistan. An American-led ground attack said to have killed at least 15 in Pakistani territory Wednesday sparked outrage and embarrassed Zardari's party.
Government ministers hailed Zardari's expected victory as a triumph for democracy nine years after Musharraf seized power in a military coup.
Musharraf, a former general, stepped down from the army last year, but only after imposing a state of emergency to fend off legal challenges to winning another term, this time as a civilian head of state.
Zardari says he will give some of the powers accumulated by Musharraf back to Parliament, but has not made clear how far he will go, sustaining concern that one strongman is replacing another.
Interior Ministry chief Rehman Malik said Saturday's bombing was an attempt to upset the progress of a country riven by ethnic and sectarian divides toward a more stable democratic federation.
If a reported Taliban claim of responsibility proves correct, "They'll have to pay for it," he said.
Like his late wife, Zardari is generally considered a pro-West liberal, and he is not expected to change Pakistan's commitment as an ally in the U.S. war on terrorism despite the recent raid and suspected U.S. missile strikes along the border.
Zardari and senior party officials have matched Musharraf's tough line against terrorism, insisting the battle against militants is Pakistan's own war. But a key test will be how much clout Zardari wields over Pakistan's powerful military, which has failed to halt the Taliban's rise in the nation's northwest despite stop-start battles.
The president has the power to dissolve Parliament and appoint army chiefs, and chairs the joint civilian-military committee that controls Pakistan's nuclear weapons.
A horse-loving aristocrat who has spent about 11 years in prison on corruption allegations that never resulted in a conviction, Zardari has surprised many with his ability to concentrate power since his wife was killed in a December gun-and-bomb attack and he inherited her party's leadership.
After ex-Prime Minister Nawaz Sharif's party switched to the opposition last month, Zardari quickly won support from smaller parties, suggesting he could give the country some stability as it faces economic challenges that include soaring inflation, power shortages and widening trade and budget deficits.
Saturday's voting bore that out.
A tally by The Associated Press of the results showed Zardari with 488 of the 685 votes, based on a formula that gave each of the four provincial assemblies equal representation and left most of the say with federal lawmakers.
Saeed-uz-Zaman Siddiqui, a former judge nominated by Sharif's party, was second with 153. Mushahid Hussain, a senator from the pro-Musharraf party routed in February parliamentary elections, was last with 44.
The Election Commission was expected to certify the results later Saturday so Zardari can be sworn in Sunday.
Information Minister Sherry Rehman called it a historic day with a tidal wave of support for both democracy and the People's Party.
"We have seen the legacy of Mohtarma Benazir Bhutto come alive once again in the voice of the people through the four provinces, the Senate and the National Assembly of Pakistan," Rehman said. "The candle of democracy lit by her with her martyrdom is still kindling."
Zardari, the son of a landowning businessman and tribal chief from the southern province of Sindh, wed Bhutto in an arranged marriage in 1987. Many Pakistanis call him "Mr. 10 Percent," a reference to accusations he pocketed commissions on government contracts during her two terms as prime minister.
After Bhutto was killed, Zardari returned to Pakistan from exile, seized the reins of her party and led it to victory in the February elections.
Zardari's party and that of Sharif - historical rivals - formed a coalition which quickly crumbled once they forced out Musharraf with the threat of impeachment.
Sharif has pledged to be constructive in opposition, but continues to call for the reinstatement of Supreme Court judges purged by Musharraf.
Three of the judges were sworn back into the court Friday, but Zardari has blocked the return of ousted Chief Justice Iftikhar Mohammed Chaudhry, who had questioned a corruption amnesty granted by Musharraf that quashed long-standing cases against Zardari.
Associated Press writers Munir Ahmad, Asif Shahzad, Nahal Toosi and Paul Alexander in Islamabad and Riaz Khan in Peshawar contributed to this report.