Metin Bozkurt, one of the founding members of the İyi (Good) Party, was attacked by a group of eight unidentified individuals in İstanbul, the Cumhuriyet daily reported on Thursday.
He is being treated at a local hospital. A picture of him taken after the incident shows significant injuries, including to his face.
The attack was captured by surveillance cameras in the parking lot where it took place.
A number of Turkish journalists and main opposition leader Kemal Kılıçdaroğlu were also the targets of physical attacks in the first half of the year.