"I was impressed by some of the things that he said about the challenges that Pakistan faces, about the centrality of fighting terrorism, and about the fact that the terrorism fight is Pakistan's fight and also his very strong words of friendship and alliance with the United States."
Zardari is co-chairman of the Pakistan People's Party, formerly led by his wife, Benazir Bhutto, who was assassinated in December 2007.
Zardari's party already heads a fragile coalition government which, although still in office, recently lost the backing of Sharif's party.
He defeated retired chief justice Saeed-uz-Zaman Siddiqui, who was backed by Nawaz Sharif, a former prime minister, and Mushahid Hussain, a close aide of Pervez Musharraf, who resigned weeks ago as Pakistani president.
Australia, an ally of the US in its ongoing "war on terorism", also welcomed the "democratic resolution" of Pakistan's leadership.
It urged Zardari on Sunday to focus on security issues, particularly in the Afghan border region.
"That's good in the sense the Pakistani democratic and parliamentary process has resolved that without a need for intervention from the military so we welcome that," Stephen Smith, the Australian foreign minister, told Sky News.
Australia has about 1,000 troops in Pakistan's neighbour Afghanistan.
Zardari, 53, is expected to be sworn in as Pakistan's president on Monday.
In a short television address, Zardari said his triumph was a victory for democracy, a reference to Musharraf, an army general whose August 18 resignation set the stage for the election.
Zardari will take charge of a country that has been riven by the Pakistani Taliban fighting, with nearly 1,200 people killed in bombings and suicide attacks in the past year.
The problem was underscored in the northwestern city of Peshawar during voting on Saturday, when a suicide car-bomber rammed a police checkpost killing 16 people and wounding more than 80.
The economy is also in trouble with rampant inflation and a plunging stock market that has lost around 40 per cent of its value since January, in a country already reliant on foreign aid.
Talat Masood, a Pakistani political analyst, told Al Jazeera that it was "ironic that Zardari is going to be Pakistan's president".
"A wave of events have pushed him into this position from spouse to the president of Pakistan.
"There is no doubt he has a controversial past and his reputation is soiled. He will have to work very hard to improve his reputation."
Al Jazeera's Kamal Hyder in Islamabad said there was concern about whether or not the new president would now relinquish some of the powers held by Musharraf.
"Musharraf was the military chief and had supreme powers, but a civilian president will not likely have those powers," he said.
"One of the PML-N's leaders said that an act of parliament would be needed to remove the powers taken up by Musharraf. If they are not taken away, it will just be continuation of one-man rule."
Hyder added: "Masood said that Pakistanis were sceptical about Zardari, but they want the democratic process to move forward and that "this selection is part of that process
"The only thing is whether he will do good for Pakistan with this power or not."