The attackers, who were riding a motorcycle, shot and killed Muhammad Farooq Gandapur, a former member of an anti-Taliban militia, at Rori in Dera Ismail Khan district, police officials said.
The killers managed to escape by taking advantage of the darkness.
Eight members of pro-government "peace committees" or anti-Taliban militias have been killed in targeted attacks in Dera Ismail Khan and nearby Tank over the past two years.
The banned Pakistani Taliban have killed scores of pro-government elders and members of private militias in the country's northwest since 2008.