Selahattin Demirtas and Figen Yuksekdag were detained at their respective homes as part of a counter-terrorism inquiry, the Interior Ministry said in a statement. At least nine other MPs from the HDP were also taken into custody.
"The HDP MPs Ferhat Encü, Leyla Birlik, Selma Irmak, Abdullah Zeydan, Selahattin Demirtaş, İdris Baluken, Figen Yüksekdağ Şenoğlu, Sırrı Süreyya Önder, Ziya Pir, Gülser Yıldırım, Nursel Aydoğan were detained" the statement read.
It said, İmam Taşçıer and Nihat Akdoğan were still sought by the police and Faysal Sarıyıldız and Tuğba Hezer Öztürk were belived to be abroad.
Meanwhile social networks could not be accessed from inside Turkey. Twitter, Facebook, YouTube and Whatsapp were reported to be inaccessible shortly after the detentions, even when users tried to circumvent restrictions using a virtual private network (VPN). Demirtas had tweeted about his arrest before the sites were restricted.
Last month, the co-mayors of Turkey's largest Kurdish-majority city were detained, also as part of a terrorism investigation. Police searched the HDP's head offices in central Ankara as well as making the arrests.
The HDP entered the Turkish parliament for the first time last year, when it won 59 seats and became the country's third-largest party.
Turkish politicians normally have immunity from prosecution, but this was removed from the HDP earlier this year.