Nawaz Sharif, leader of the PML-N, on Monday afternoon quit the coalition government, led by presidential hopeful Asif Zardari.
An ultimatum given to the ruling party by its coalition partner regarding the reinstatement of 60 judges expired on Monday.
Earlier in the day, Sharif met with top officials in his party to decide whether to quit the ruling coalition in accordance with his ultimatum.
"There is no need for the party to be part of the coalition government, if one party is taking decisions unilaterally," Siddiq Al-Farouq, a spokesman for the PML-N, said yesterday according to the local press.
The PML-N, which constitutes the second largest party in Pakistan, was not satisfied with an announcement made by Prime Minister Yousuf Raza Gilani, a member of the ruling PPP party. Gilani said the government would restore the sacked judges, but did not say when this would be carried out.
PPP leader Asif Zardari wants to keep 60 judges, who were appointed last year by former president Pervez Musharraf. The judges backed legislation that withdrew corruption charges against Zardari and his late wife Benazir Bhutto, paving their return to Pakistan and to power.
Meanwhile, 13 people were killed in violence in the Swat Valley on Sunday, while two more bodies were retrieved from the rubble of the Charbagh police post, blown up in a suicide attack on Saturday.
More then 100 people have been killed in the past week in terror attacks across Pakistan.