Pakistani politician Makhdoom Javed Hashmi, addressing fellow lawmakers, called the country's first democratically elected government and transfer of power historic, Dawn.com reported.
"This day is a historic day for Pakistan. Only democracy can hold Pakistan together," said the Pakistan Tehrik-i-Insaf leader, who won 31 votes in the election for the office. "Sharif's victory is associated with Pakistan's victory."
Hashmi also spoke about the contentious issue of U.S. drone airstrikes in Pakistan's tribal region, which Pakistan claims killed many innocent people.
Tribal leaders have called for an "end to U.S. drone strikes in Pakistan," he said. "We will stand firmly in our resolve to oppose this menace."
He said he hoped Pakistan's new government would give smaller provinces greater representation, Dawn.com said.
He pledged his party would support the government in the "good initiatives" it takes, but would assume the role of a strong, firm opposition party in the National Assembly.
Sharif was the first person elected prime minister for a third time, GEO News reported. Previously a candidate was barred from holding public office for more than two terms.
Sharif was first elected prime minister in 1990 but pressure from military officials in 1993 forced him to resign.
He was elected prime minister for a second time in 1997, but was jailed then driven into exile when the chief of army staff toppled the Sharif government.
Nawaz Sharif returned to Pakistan in November 2007 and his party became part of the hung parliament after the 2008 elections, forcing the Musharraf to resign from office or possibly face impeachment.