Initial reports suggest that Rashid Rehman Khan's car was targeted by the gunmen near Kachehri Chowk in Multan.
Khan was a coordinator for the Human Rights Commission of Pakistan (HRCP).
The senior lawyer was representing a blasphemy accused and had complained that he had been receiving threats on his life.
The HRCP had voiced serious concern over the threats extended to Khan.
Lawyers defending blasphemy accused are often seen at the receiving end of extremists and fundamentalists.
In some cases, even judges are scared to hear the matter due to threats from fundamentalists and extremist organisations.