Army chief Gen Ashfaq Parvez Kayani and Chief Election Commissioner Fakhruddin G Ebrahim were among those who exercised their right to franchise shortly after polling began at 8 am.
Footage on television showed Kayani walking into a polling station in Rawalpindi to vote.
Long queues were seen outside thousands of polling stations across the country despite fears of attacks by the Taliban, which had said that it would carry out attacks, including suicide bombings, on election day as it considers the polls part of an "infidel system" of democracy.
Threats and attacks by the banned Tehrik-e-Taliban Pakistan forced three major parties - Pakistan Peoples Party, Awami National Party and Muttahida Qaumi Movement - to dramatically curtail their campaign.
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More than 86 million people are registered to vote in the polls though elections in Pakistan have traditionally registered low turnouts.
Only 44 per cent of the electorate voted in the last general election in 2008.
A total of 4,670 candidates are standing for parliamentary elections while nearly 11,000 are running for the four provincial assemblies.