The president, Bilal Kasi, was killed when some unknown gunmen attacked his vehicle in Manno Jan area of Quetta.
No group has claimed responsibility for the attack yet.
A heavy contingent of police and paramilitary troops rushed to the blast site and cordoned it off for investigations.
Pakistani Prime Minister Nawaz Sharif condemned the blast and vowed to root out militancy from the country.
The country's Army Chief Raheel Sharif arrived at Quetta to ask after the health of the injured people.
The Balochistan government announced a three-day mourning and the national flag will fly on half-mast during the mourning days in the province.
The explosion caused a chain reaction from the circles of lawyers in the country.
Lawyers in Balochistan and the country's southern port city of Karachi boycotted court proceedings.
The Pakistan Bar Association condemned the attack and announced a three-day mourning.