Taliban attacks have so far killed more than 100 people on the campaign trail and forced the main parties in the outgoing government, singled out by the insurgents for their alliance with the United States, to scrap major rallies.
The race has been dominated by opposition leader Nawaz Sharif, head of the Pakistan Muslim League-N (PML-N) and former cricket star Imran Khan, who is looking to make a breakthrough for his Pakistan Tehreek-e-Insaf (PTI) party.
Sharif, a steel tycoon, is considered the front-runner and tipped to become the first politician to serve three terms as prime minister. He was first in the post from 1990-93, until he was sacked for corruption, and from 1997-99, when he was deposed by a military coup. Sharif: The tycoon bidding for third Pakistan term
Khan, who won only one seat in 2002 and boycotted polls in 2008, has led an electric campaign, galvanising the middle class and young people in what he has called a "tsunami" of support that will propel him into office.
File photo of Imran Khan. (AFP Photo)
The former Pakistan cricket captain suffered head injuries after falling from a lift winching him up to the stage for an election rally on Tuesday, but recovered to make an appeal for voter support from his hospital bed.
The main outgoing Pakistan People's Party (PPP) has run a lacklustre, rudderless campaign without a leader. Its election advertising still stars Benazir Bhutto, its charismatic prime minister assassinated in 2007.
Her son, Bilawal, is too young to run for parliament and Taliban threats have prevented him from addressing public rallies. His father, President Asif Ali Zardari, is barred from campaigning as head of state and is anyway deeply divisive and unpopular.
Bilawal: Pakistan's absent dynastic heir
Zardari: Pakistan survivor, party in crisis
The polls are considered critical to strengthening democracy in Pakistan, marking the first time that an elected civilian government completes a full term and hands over to another in a country ruled by the army for half its existence.
Pakistan's more than 86 million voters have the choice of 4,670 candidates standing for the 342-member lower house of parliament and nearly 11,000 people running for four regional assemblies.
File photo of Asif Ali Zardari. (AFP Photo)
More than 600,000 security personnel will be deployed across the country to guard against Taliban strikes and around half the estimated 70,000 polling stations have been declared at risk of attack.
Turnout will be crucial. Commentators are divided on whether a wealth of enthusiastic first-term voters and Taliban threats will make turnout higher or lower than the 44 percent at the last elections in 2008.
"I want every person in this nation to have equal living standards, equal education, equal career opportunities," said Rohail Khan, 21, a student in the southwestern city of Quetta, excited about voting for the first time.
The main issues are the tanking economy, an appalling energy crisis which causes power cuts of up to 20 hours a day, the war on Islamist militants, chronic corruption and the dire need for development.
Khan has sought to put policies and issues at the front of the campaign, promising to stamp out corruption, but personality politics and kinship ties traditionally determine voting in Pakistan. Imran Khan: Cricket star poised for political breakthrough
Sharif has presented himself as a statesman-in-waiting, the man who presided over economic growth in the 1990s and the man who knows how to deliver.
File photo of Nawaz Sharif. (Reuters)
Both he and Khan have backed talks with the Taliban and criticised US drone strikes against Islamist militants, although it remains unclear if or how policy towards extremism would change under a new government.
Raza Rumi, the director of the Jinnah Institute think tank, says the Taliban threat to the campaign has been alarming.
Key facts about Pakistan's general election
"It is the first time that non-state actors are even now determining the course of elections. That is a major worry," he said.
"The surprise is Imran Khan's growing support in the country. Whether he wins or not is a separate issue, but the fact that he mobilised so many people, he gave confidence to so many people, is good for the democracy."
Facts about Pakistan
If PML-N and PTI perform well, they are likely to face criticism that they were helped to their victories by the Taliban, which singled out the PPP and its secular partners, the Awami National Party (ANP) and the Muttahida Qaumi Movement (MQM).
But Taliban spokesman Ehsanullah Ehsan, referring to PTI and PML-N, told AFP: "If they also come into conflict with Islam, then we will decide to target them."
Supporters of Imran Khan, chairman of political party Pakistan Tehreek-e-Insaf (PTI) chant slogans during an election campaign rally in Lahore. (Reuters)