An additional 450,000 police were also assigned to provide security, according to election officials. The military presence is just the latest controversy in a bitter campaign season that has seen accusations of "pre-poll rigging", the expansion of hardline religious parties, and a string of bloody militant attacks that have killed more than 180 people, including three candidates.
Despite the controversies and bloodshed, political parties continued to criss-cross the country in the final days before the polls, holding dozens of rallies in key battleground areas.
The contest has largely been distilled to a two-party fight between jailed former prime minister Nawaz Sharif's incumbent Pakistan Muslim League-Nawaz party, and cricket legend Imran Khan's Pakistan Tehreek-e-Insaf.
"Our predictions are very murky right now," Bilal Gilani, executive director of Gallup Pakistan, told AFP, adding that a huge chunk of voters remain undecided.
"It's still up for grabs."
'We will fight'
At a distribution centre in Lahore, election workers complained of general discord and delays in the delivery of ballot boxes.
"I have been performing election duty for the past 22 years and I have never seen such a disorganised election my whole life," said one worker who asked to remain anonymous, adding that the troops overseeing the process had done little to help.
A day before the polls, voters were largely split in Lahore, the capital of Punjab - Pakistan's most populous province and long a PML-N stronghold that is being fiercely challenged by Khan's PTI.
"I am supporting Imran Khan because he is the best choice for Pakistan. We should give him a chance," said Muhammad Wasim, 32, pointing to what he described as the success Khan's party has had in governing northwestern Khyber-Pakhtunkhwa province.
Others cited the improvements in infrastructure under the PML-N in the sprawling city in the east of the country, vowing to stick by the party hit by several corruption convictions ahead of the election.
"They have served the masses, they have put an end to... (power cuts) and given us better facilities including roads, transport and education," said shopkeeper Muhammad Nawaz, 45.
Political parties held their final rallies Monday night - before campaigning was suspended - in a last-ditch attempt to energise voters.
"I am giving this task to all of you: wake up early on the 25th and cast your vote," Khan told thousands of PTI faithful in Lahore.
In southern Punjab, PML-N leader Shahbaz Sharif - the former premier's brother - said victory was "certain".
"Despite all the odds, PML-N is winning the July 25 polls," he was quoted as saying by Pakistani media.
At a PML-N rally in the Rawalpindi, anger simmered over what participants said was engineering by "the establishment" Some vowed to take to the streets if directed by their leaders. "After the election, we will fight," said PML-N supporter Aftab Anjum, 67. "We are all ready."