Handry Masih was elected to the member of Balochistan's provincial assembly from the province's ruling National Party.
The lawmaker was shot by the guard near his home in Nawa Kalay area of the city, where he met the people of his constituency on the weekends, Dunya TV reported.
He was taken to hospital where he died.
One of his nephews was also injured in the attack but he is stable and out of danger.
The motive of the attack was not known as yet.
Pakistan's Christian minority is constantly persecuted and attacked by hardline Islamist elements.