Mr Nawaz Sharif pulled out of the government over the issue of judges
Eight of the judges sacked last November by former Pakistani President Pervez Musharraf have been reinstated.
They took their oaths at the governor's house in Karachi. Reports say seven or eight more may be sworn in next week.
Mr Musharraf sacked some 60 judges, including Chief Justice Iftikhar Chaudhry, but some were restored later.
Former Prime Minister Nawaz Sharif pulled out of the ruling coalition on Monday amid a dispute about how to restore the judges.
Mr Sharif's PML-N party wants all the sacked judges to be reinstated in one go, through an executive order that declares their sacking illegal.
The BBC's M Ilyas Khan in Karachi says the party's views are also supported by a lawyers' movement that is campaigning for the restoration of the judiciary as it existed on 2 November 2007 - one day before Mr Musharraf introduced emergency rule and sacked the judges.
The leader of the ruling Pakistan People's Party (PPP), Asif Zardari - the husband of assassinated former Prime Minister Benazir Bhutto - has promised to restore the judges but under a fresh oath.
Mr Zardari has said the top judge will ultimately get his job back too, but few analysts believe this, reports the BBC's Barbara Plett in Islamabad. They say the government sees him as too willing to challenge the establishment, and too close to the politics of the Muslim League.
Analysts say the reinstatement of judges by the PPP is likely to weaken the lawyers' movement and raise questions over PML-N's decision to quit the alliance.