He was on his way to the Balochistan High Court (BHC) when he was targeted by armed motorcyclists.
Shar was rushed to Quetta Civil Hospital but he succumbed to his injuries while on the way to the medical facility.
The site of the attack was cordoned off following the incident and an investigation initiated to arrest the culprits.
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Dawn quoted police surgeon Ayesha Faiz as saying that the superior court lawyer sustained 16 bullets in the attack.
Meanwhile, Quetta Bar Association President Abid Kakar announced to halt proceedings of the BHC and lower courts as he also announced a three-day mourning over the death.
'Imran responsible for murder'
Special Assistant to the Prime Minister (SAPM) Ataullah Tarar termed PTI chairman Imran Khan "directly responsible" for the lawyer's killing.
On May 29, a division bench of the BHC had heard Shar's plea, wherein he had sought Imran's trial under Article 6 of the Constitution.
He had pleaded that the ex-premier violated the Constitution by asking President Arif Alvi to dissolve the National Assembly, and so he should be tried under Article 6.
Addressing a presser in Islamabad, Tarar alleged that the PTI chief "got the lawyer killed to protect himself from the treason case and he will be nominated in the murder case."
PTI rejects assertions
The PTI rejected the "baseless and futile allegations", and demanded that a case instead be filed against Prime Minister Shehbaz Sharif and Interior Minister Rana Sanaullah for the murder.
In a Twitter post, the party asked the Supreme Court to take urgent notice of the incident and the 'false allegations' being made against the former premier.