The opposition leader, Nawaz Sharif, sealed his place as the most popular politician in Pakistan this month when he defied his house detention and led a triumphant protest that forced the government to restore the country’s chief justice.

Now, as the Obama administration completes its review of strategy toward the region this week, his sudden ascent has raised an urgent question: Can Sharif, 59, a populist politician close to Islamic parties, be a reliable partner? Or will he use his popular support to blunt the military’s already fitful campaign against the insurgency of the Taliban and al-Qaida?

A former two-time prime minister, Sharif once pressed for Islamic law for Pakistan, tested a nuclear bomb and was accused by his opponents of undemocratic behavior during his tenure in the late 1990s. That political past has inspired distrust here and in Washington and left some concerned that Sharif is too close to the conservative Islamists sympathetic to the Taliban to lead a fight against the insurgents.

His supporters and other analysts say that Sharif is now a more mature politician, wiser after eight years of exile in Saudi Arabia and London, and that he is eager to prove he can work with Washington and to put his imprint on a workable approach toward stabilizing Pakistan.

“If Washington is going to carry Pakistan, it is important they do it with popular support,” said senator Enver Baig, a disaffected member of the Pakistan Peoples Party, who resigned from a party post last month. “There’s the realization in Washington that he is the next guy we should talk to.”

Some diplomats and analysts argue that Sharif’s affinity with the Islamic parties could now be an asset as Washington tries to win Pakistani support to fight the militants.

“We, and all sensible Pakistanis, need the support of Saudi Arabia and the more moderate Islamist parties, particularly Jamaat-e-Islami, if we are ever going to tame the jihadis,” said a former American ambassador to Pakistan, Robert Oakley. “Nawaz’s good standing with them is very, very important.”