The 60-year-old Khan is shaping up to be the biggest wildcard in the May 11 parliamentary election - the first transition between democratically elected governments in a country that has experienced three military coups.
After over a decade of trying to gain a foothold in Pakistani politics, he has finally elbowed his way into the big league. Casting himself as a populist anti-corruption crusader challenging the traditional political elites, he is seen as a threat to the two parties that have long dominated elections.
Khan has almost mythical status in cricket-crazy Pakistan as the captain of the national team that won the 1992 World Cup - the only time the country has claimed the sport's highest prize - and polls as the nation's most popular politician by a wide margin.
But it's uncertain how effective he will be in converting his personal appeal into votes for his party.
Much of Khan's support has come from young, middle class Pakistanis in the country's major cities, a potentially influential group. Almost half of Pakistan's more than 80 million registered voters are under the age of 35, but the key question is whether Khan can get his young supporters to show up at the polling booth on election day.
"This is going to swing the election," Khan told The Associated Press in an interview before the rally. "The youth is standing with us and change."
Khan, one of the few Pakistani politicians with a squeaky-clean image, broke into the political mainstream in the last 18 months with a message that capitalizes on widespread discontent with the country's traditional politicians. They are seen as more interested in lining their pockets than dealing with pressing problems facing Pakistan, such as stuttering economic growth, pervasive energy shortages and deadly attacks by Islamist militants.
On foreign policy, he has also struck a chord by criticizing Pakistan's unpopular alliance with the United States and controversial American drone attacks targeting al-Qaeda and Taliban militants in the country's tribal region that borders Afghanistan.
His message has helped him rally huge crowds in Pakistan's major cities, including more than 100,000 people who showed up Saturday in the heart of Lahore, the capital of Pakistan's most populous province, Punjab. The province will be the main battleground in determining which party wins enough seats in the National Assembly to form the country's next government.
"We want to clean up corruption. We want justice. We want electricity, and only Imran Khan can do it," said Mohammed Wasim, a 21-year-old student from Lahore and one of many first-time voters attending the rally near the country's towering national monument, the Minar-e-Pakistan.
Many of the people at the rally were middle class youths like Wasim who danced to blaring music over loudspeakers and waved the red, white and green flag of Khan's party, Pakistan Tehreek-e-Insaf, or the Movement for Justice. But plenty of older Pakistanis, some of whom had switched from other parties out of frustration, also turned up.
Khan hopes the momentum from the rally will push forward what he calls his political "tsunami" and help his party win a majority of the 172 National Assembly seats that are up for election. That would allow Khan to form the next government and position him to become prime minister.
He is up against the two groups that have for decades dominated the country's politics, the Pakistan People's Party, which led the most recent government, and the main opposition party, the Pakistan Muslim League-N. Both have broad alliances with local leaders who use political patronage, such as government jobs and contracts, to shore up support.
"The reason why we are in politics is to break the stranglehold of these two parties who have plundered this country," Khan told the AP.
Many analysts are less bullish and believe Khan's party, PTI, will win 20-40 seats, many of them in urban areas of Punjab. Many predict the PML-N, which is led by former Prime Minister Nawaz Sharif, will benefit from broad discontent and lead the polls, while the PTI will come in third behind the recently ruling PPP. The conventional wisdom is that no party will win a majority of the seats, and the PML-N will end up having to put together a weak coalition government.
"I think third place is the safest bet for Khan's party, but if he could gain second, which is not impossible, it would be a big political revolution for the country," said Rasul Baksh Rais, a political science professor at Lahore University of Management Sciences.