But in taking his campaign to force out Nawaz Sharif on to the streets of Islamabad, Khan may have overplayed his hand.
This weekend his crowd of followers was already thinning out, and without overt support from the military his protests are unlikely to be a game-changer.
Thousands showed up for his rally on Saturday, but some supporters grumbled they had slept out in the rain while Khan relaxed in his nearby mansion.
"The path he's chosen is one of protest," said Samina Ahmed, South Asia director of the Brussels-based International Crisis Group think tank. "Now the question is: does he have a strategy beyond the protest?"
Even if the protest movement fizzles, however, Sharif will have been left weakened and less likely to challenge the country's powerful military on security and foreign policy, which Pakistan's generals have long considered to be their domain.
Read: Tens of thousands hold anti-PM rally in Pakistan
Sparring with the generals
Khan accuses Sharif of rigging last year's election, which marked the first democratic transition in Pakistan's turbulent history, and last week vowed to occupy Islamabad until the prime minister resigns.
The government has warned that his protest, and another led by fiery cleric Tahir ul-Qadri, could destabilise the nuclear-armed nation of 180 million, which has seen a succession of military coups and is struggling to stifle a Taliban insurgency.
It fears Khan is trying to force a confrontation so the army will once again intervene, or that the military is manipulating Khan from behind the scenes.
There is no doubt that the military brass dislike Sharif, who stormed back to power for a third time last year after his party won a clear majority of parliament's seats.
Sharif has put former military head Pervez Musharraf, who abruptly ended his last stint as prime minister in a 1999 coup, on trial for treason.
He has also dithered over a military offensive to quash the Taliban, sided with a media group that accused the military of shooting one of its journalists and sought reconciliation with arch-foe India, the perceived threat that the army uses to justify its prominent position.
One political analyst said it was unlikely Khan was encouraged by the army to challenge Sharif, and much more likely that Khan had decided to pounce because the prime minister's sparring with the generals had left him vulnerable.
"If the relationship with the military had not gone out of kilter, then Imran would not have seized this opportunity," said the analyst, who declined to be named due to the sensitivity of the issue. "He saw Sharif was on shaky ground."
In recent months, Sharif's resistance to the military has softened. An anti-Taliban offensive began in June and the treason trial against Musharraf has quietly ground to a halt.
The army has not commented publicly on the protests, but insiders say it has no appetite for forcing Sharif out - which would involve a showdown with Pakistan's increasingly powerful judiciary.
That makes it all the more likely that Khan's protest will fizzle out unless he forces a confrontation.
"When I asked him, 'what's your exit strategy?', he said: 'I play to win,'" said the analyst. "It's a sportsman's calculus."
Read: Shots fired at Imran Khan, anti-govt protesters clash
Playboy to politician
For decades, the charismatic 61-year-old Khan was lauded for his sporting prowess and his charitable work. An Oxford graduate, Khan captained his country to its only cricket World Cup victory in 1992. As a philanthropist, he built a cancer hospital and aided victims of a flood disaster in 2010.
He wed the blonde daughter of a British billionaire financier, and many in this conservative Muslim country were titillated by tales of his playboy lifestyle.
Although he first dabbled in politics in the mid-1990s, until last year his Pakistan Tehreek-e-Insaaf (PTI) party had only ever won a single parliamentary seat - his own.
But voters flocked to Khan's banner of reform and his image as a conservative maverick. He denounced the corruption and tax evasion of mainstream political parties and blasted Washington for its deadly drone strikes in militant-infested borderlands.
The 2013 polls made Khan's party the third-largest bloc in parliament, giving him control of 34 seats out of the 342.
Read: Pakistan govt splits protesters on I-Day
Khan and the military
In the past, the military may have seen Khan as a useful figure to ensure it remains the real centre of power.
Had Sharif not won so handsomely, Khan would have been a forceful opposition in parliament, keeping mainstream parties on the defensive and acting as a safety valve for popular anger over the graft and incompetence of the political class.
But the military also see him as a nuisance for seeking an end to the fight against the Taliban and a negotiated peace. He has sometimes been ridiculed as "Taliban Khan" for his views on the insurgency and hostility towards US drone strikes.
Another reason for the military's reluctance to back Khan may be the performance of his party in Khyber Pakhtunkhwa province, home to the Taliban insurgency, since it took power there last year.
Khan's provincial government has hiked the education budget and tried to reform the police. It has also legislated on citizens' rights to government information and services such as gas, power and water, and forbidden officials to engage in business that conflicts with their duties.
But residents say implementation of those laws is spotty, and some other promised reforms have failed to materialise.
Now, as Khan's supporters camp out in Islamabad, some in his own provincial capital of Peshawar are becoming impatient.
"We voted for Imran Khan's party in our province but they have engaged themselves in other issues," said furniture maker Mohammad Ikram.
"They should solve the problems of the people of this province first and then criticise the federal government."