Maqsood Ahmed Bhatti, the Tehrik-e-Insaf district president, was going to Lahore along with his three guards when unidentified gunmen intercepted his vehicle and opened indiscriminate fire on it, killing all of them on the spot, police said.
One passerby was also wounded in the firing. He later succumbed to his injuries in hospital.
Police described the incident a result of "old enmity" and launched an investigation into the incident.
In another incident, PTI's women wing president Lahore Neelam Ashraf's son was found dead in his car under mysterious circumstances today.
Police have taken three suspects into custody.