63-year-old Mulk, Supreme Court's senior most judge, took over from his predecessor Tassaduq Hussain Jillani.
President Mamnoon Hussain sworn in the new chief justice at a ceremony attended by Prime minister Nawaz Sharif, his cabinet members and other senior officials.
It would be interesting to see Mulk's ties with the government.
Over the years, Pakistan's judiciary has been politically active after ex-chief justice Iftikhar Muhammad Chaudhry was sacked by the then-military ruler General Pervez Musharraf in 2007, and was later reinstated in 2009 after a nation-wide protest by lawyers.
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After Chaudhry demitted office December 2013, his successor Jillani too laid emphasis on cases of public interest and individual complainants.
In his farewell speech for Jillani on Thursday, Mulk indicated an end to years of judicial activism that had pitted the government, military and judiciary against each other.
"The task of the judiciary is a dispassionate reading of the law unaffected by personal biases," a transcript of his speech on the Supreme Court's website said.
"Considerations of Constitution and the laws alone should guide the judge and personal sense of justice must be strictly curtailed," it said.
"Institutions need to work in harmony with one another and it is their constitutional duty to desist from undue interference in the functioning of other pillars of state. In case, institutions do not respect the trichotomy of power, we fear that the rights of the people will be violated and disregarded," he said.