A three-member bench comprising Chief Justice of Pakistan (CJP) Umar Ata Bandial and Justices Ijazul Ahsan and Munib Akhtar announced its decision on the petition filed by PML-Q leader Parvez Elahi against Mazari's ruling.
According to the decision, Hamza lost its status as the "trustee" Punjab chief minister while Elahi, who has PTI's backing, will take over the position.
"Deputy speaker's ruling is illegal. There is no legal justification for the deputy speaker's ruling," said the apex court.
The court ordered Punjab Governor Baligh ur Rehman to administer the oath to Elahi at 11:30pm. It said if the governor refuses to perform his duties, then President Dr Arif Alvi will administer the oath.
"Hamza Shahbaz and his cabinet should leave their posts immediately," the top court ruled.
The court ordered that all advisers and assistants appointed by Hamza should also leave their posts.
During the election held on Friday, Mazari had rejected votes of 10 PML-Q lawmakers cast in Elahi’s favour, citing a letter written by party President Chaudhry Shujaat Hussain, in which he had instructed them to vote for Hamza instead.