Awami National Party office-bearer Zainul Abideen was attacked and killed by unidentified gunmen who opened fire on his vehicle near the Matric Board Office in North Nazimabad on Wednesday.
According to a spokesman for ANP Sindh, a companion of Zainul Abideen was also injured in the incident.
ANP Sindh President Shahi Syed condemned the killing and demanded the killers be arrested immediately.
Provincial Home Minister Mansoor Wasan has summoned a report from the IG police.
Following the killing, violence erupted in several areas of the city, including Empress Market, Bohri Bazar and NIPA Chowrangi. A man was also killed in Lasbella when unidentified armed men opened fire on him.
Meanwhile, two cars and three motorcycles were set on fire in the Teen Hatti area. A passenger bus was also burnt on Nishtar Road. Shops, petrol and CNG stations were shut down as violence spread to various parts of the city.
Earlier, Home Minister Manzoor Wassan said a judicial inquiry would be held into the loss of life and burning of vehicles in incidents of violence that triggered in the metropolis following the killing of two Muttahida Qaumi Movement (MQM) workers on Tuesday.
He also ordered an imposition of ban on carrying arms across the province.