Fakhrul Islam, a 46-year-old ethnic Pushtun member of the Mutahhida Qaumi Movement (MQM) Party, was shot by gunmen on motorcycles on the outskirts of Hyderabad on April 11.
A spokesman for the Pakistani Taliban, Ehsanullah Ehsan, said his group was behind the killing of Islam.
Militants from the Pakistani Taliban have threatened the main secular parties, including the MQM, for the political parties' criticism of Islamic insurgents.
Ehsan vowed that the militants would continue to target candidates from those parties.
Pakistani interim Prime Minister Mir Hazar Khan Khoso ordered an immediate tightening of security for all candidates in the May 11 general election.
But Islam isn't the only one affiliated with MQM who has been killed in recent days, there have been others.
The MQM is a secular political party that condemns extremism and religious militancy. It's the third largest party in Pakistan.
The Pakistan Taliban won't be happy until they have removed all vestiges of secular leadership in that country.