Asif Ali Zardari, the widower of former Pakistani prime minister Benazir Bhutto, was sworn in as president on Tuesday, in what allies and investors hoped was a step toward stability after months of uncertainty.
Mr Zardari swept an election on Saturday when members of the two-chamber parliament and four provincial assemblies voted on a replacement for former army chief Pervez Musharraf, who resigned in August, nine years after taking power in a coup.
A spokeswoman for Zardari's Pakistan People's Party said the new president would strengthen democracy and help the poor.
"Asif Ali Zardari is a shield, protection to strengthen democracy and provide relief to the masses," the spokeswoman, Farzana Raja, told state television shortly before the swearing-in ceremony.
"Democracy will work and this government will complete its five years and you'll see after five years, Pakistan will appear on the world map as new country with new hope," she said.
Investors and Pakistan's allies, led by the United States, hope the election will bring some economic stability after months of political turmoil and rising militant violence.