Unidentified gunmen attacked the lawyer, Samiullah Afridi, in his car near the city of Peshawar on Tuesday, said Mian Saeed, a police superintendent in Peshawar.
Two different militant groups claimed responsibility for the killing.
The lawyer had represented Dr. Shakeel Afridi, who was convicted of treason in 2012 by a Pakistani tribal court and is now serving a 23-year prison sentence
. The two men are not related.
The doctor helped the CIA set up a fake vaccination campaign in an attempt to collect DNA samples from relatives of Bin Laden in an effort to verify his presence in a compound in the Pakistani city of Abbottabad.
The Qaeda leader was killed in a U.S. raid
on the compound in May 2011.
Claims from two groups
It was unclear which of the two groups claiming responsibility for the attack was actually behind it.
Fahad Marwat, a spokesman for the militant group Jundallah, told CNN that Afridi was on the group's hit list.
But Ehsanullah Ehsan, a spokesman for a faction of the Pakistani Taliban, said his group had carried out the assassination because Samiullah Afridi defended the doctor, whom he described as "a friend" of bin Laden's killers.
CNN national security analyst Peter Bergen said Jundallah is "kind of a splinter group" of the Pakistani Taliban that's "been around for a long time."
"They're extremely violent," he said. "They've been killing all sorts of religious minorities in Pakistan."
Last month, the group claimed responsibility for a suicide bombing
outside a Shiite mosque in the city of Rawalpindi.
Doctor 'very unpopular' in Pakistan
Bergen said Dr. Afridi is "a very unpopular figure in Pakistan" because of the perception that he was involved in helping find Bin Laden.
"And his lawyer, by extension, would also be seen as an unpopular person because of that perception," he said.
But Bergen said he didn't think the doctor played a key role in the hunt for Bin Laden.
"The idea was the doctor and his staff would take DNA samples from the Bin Laden kids as part of this 'vaccination program,'" he said. "That never happened because the kids never came out."
Although Dr. Afridi was working for U.S. intelligence, "the CIA wasn't telling the doctor, you're helping us find bin Laden," Bergen said.
After the killing of bin Laden, health workers administering polio vaccinations have come to be viewed with suspicion
by many Pakistanis. The vaccination teams have repeatedly been targeted by militants.
The latest instance came Wednesday when unidentified attackers killed one polio vaccination worker and wounded another in Bajaur agency in northwestern Pakistan, local authorities said.