Pakistan’s prime minister, Imran Khan, has lost a no-confidence vote in parliament after a dramatic week in which he violated the constitution in an attempt to stop the move going ahead.

Khan, the former premier cricketer turned pious Islamist politician, has been fighting for his political life for weeks, after losing his parliamentary majority.

On Thursday, he was delivered a blow after Pakistan’s supreme court found he had broken the law by dissolving parliament in an attempt to prevent a no-confidence vote he was expected to lose from going ahead last week.

On the court’s instructions, the vote finally took place on late Saturday night, though not before Khan’s party spent a 14 tumultuous hours trying to delay and block it in the national assembly.

The parliament’s lower house will meet on Monday to vote for a new prime minister, it was announced later on Saturday.

The opposition had accused Khan of trying to hold the constitution and government “hostage” and of treason after his party, Pakistan Tehreek-e-Insaf, attempted various means, including filibustering and legal petitions, to try to stop the vote.

The opposition stated that Khan was refusing to let the vote go ahead unless he could secure a guarantee that neither he nor his cabinet ministers would face criminal cases once they stepped down. During his time in power, Khan had jailed several opposition party figures.

As Khan took meetings with ministers and senior military figures on Saturday, many feared that he would try to get Pakistan’s powerful army to step in and declare martial law rather than hand over power to the opposition, returning Pakistan to its past dark days of military interventions in times of political instability. Fears of unrest swirled and security was beefed up around the prime minister’s residence.

As concerns over Khan violating the supreme court ruling mounted, the chief justice took the unprecedented step of asking the supreme court to be ready to open its doors at midnight, should the vote not happen. The Islamabad high court also prepared itself to hear a late-night contempt of court case.

With just 10 minutes to go before midnight, the legal deadline for the vote, the house speaker Asad Qaiser, an ally of Khan whose role it was to put forward the no-confidence vote in parliament, resigned from his post, saying he could not take part in a foreign conspiracy to oust the PM.

Instead, the speaker role was passed to another MP and, in the final moments of Saturday, after reported pressure from the military on Khan to either resign or face the vote of no confidence, Khan finally agreed to have his premiership put to parliament, though left the parliament chamber as the vote took place.

As expected, without a majority, he lost the no-confidence vote by 174 votes, thereby removing him from power over a year before his term officially ended and making him the first Pakistan prime minister to be ousted on a no-confidence vote. Fawad Hussain, Khan’s minister for information, called it a “sad day for Pakistan. The return of looters and a good man sent home.”

Khan’s loss leads the way for a new opposition coalition government, with the leader of the opposition, Shahbaz Sharif, the brother of the jailed former prime minister Nawaz Sharif, as interim prime minister. The opposition has stated its intention to hold elections in the next few months, though they are likely to be October at the earliest.

Sharif, who will be sworn in as the next prime minister in coming days, told the Guardian that the opposition had no intention of taking “revenge” on Khan and “no intention to pursue the politics of hate and divisiveness. Pakistan needs healing and should look forward.”

Sharif said they would prioritise electoral reform, with a view to holding a general election “in due course”

“The country is in all sorts of mess, thanks to the epic mismanagement of the Imran Khan government,” he said. “From paralysed bureaucracy to the foreign policy challenges to the broken economy, chaos is reigning supreme.”

Last week’s no-confidence vote was tabled by the opposition amid an economic crisis that has pummelled Khan’s popularity.

Khan shocked the opposition by instructing the deputy speaker of the house, a close ally, to throw out the vote on the basis of his allegations that it was the result of a “foreign conspiracy” to unseat him.

Khan then instructed the president, another ally, to dissolve parliament and announced fresh elections would happen within three months. He defended the move as an attempt to protect Pakistan from a western- and specifically US-led conspiracy to interfere in its affairs.

The opposition described it as a “civilian coup” and a treasonous attempt by Khan to cling to power despite losing his majority. They appealed to the supreme court, who overturned Khan’s decision.

Despite many suggesting he might resign rather than face the humiliation of a defeat in parliament, in a late night address to the country, Khan made it clear he had no intention of stepping aside voluntarily.

He called for his supporters to take to the streets in mass protest and said he would not accept any “imported” government, a veiled reference to his previous allegations that the political opposition had conspired with western powers to topple him, a charge they deny.

“What is happening with our democracy is catastrophic,” Khan said in his speech. Khan, once a national cricketing hero and international playboy, was elected in 2018 as the “modern” face of Pakistan, who had the backing of the military and promised economic prosperity and an end to corruption.

But his time in office has been blighted by economic crisis, including record inflation . He had also been seen to pander to militant Islamic groups, and during his time in office religious violence and public lynchings of those accused of blasphemy were on the rise.

Nonetheless Khan still commands fierce among his supporters and is expected to contest the next elections, though this time without the tacit backing of the military establishment.

In a Twitter post after the supreme court ruling, Khan wrote: “My message to our nation is I have always and will continue to fight for Pak till the last ball.”

Hannah Ellis-Petersen and Shah Meer Baloch in Islamabad