The PTI, which secured 116 general seats in the National Assembly in the July 25 polls is the largest party in the lower house of parliament.
The election of the Prime Minister will be held after election of the new Speaker who will supervise the election of the premier.
Mr Bhutto-Zardari took the oath as member of parliament for the first time, whereas his father returned to the house after more than two decades. Newly elected members of the three provincial legislatures took oath.
After the election of the Speaker and deputy speaker, nominations will be called for the Prime Minister.
The PTI has nominated Asad Qaisar for speaker, while opposition has named Syed Khurshid Shah of the PPP as the joint opposition candidate for the post. In an interview to news agency ANI over the weekend, when asked if India was open to a dialogue with Pakistan's Imran Khan-led government and whether India would participate in the Saarc meet that Islamabad will host this year, Modi seemed to steer clear of any definite answers.
"The Secretariat of the Chairman of Pakistan Tehreek-e-Insaaf has invited me to attend the swearing in ceremony of Imran Khan as the Prime Minister of Pakistan on August 18 at Islamabad", Sidhu said.
According to Punjab's Information and Public Relations Department, Khan also thanked Sidhu for praising him in a press conference on August 2. After the oath-taking ceremony, the speaker will prorogue the NA session until August 15, when the new speaker and deputy speaker of the assembly will be elected.