Leyla Guven and Musa Farisogullari of HDP were accused of being members of an armed terror group, while Enis Berberoglu of CHP faced charges of leaking state secrets to a newspaper.
Three former opposition party lawmakers were sent to prison early Friday, a day after parliament revoked their seats after convictions against them became final.
Those stripped of their status were Leyla Guven and Musa Farisogullari from the Kurdish Peoples' Democratic Party (HDP) and the Republican People's Party's (CHP) Enis Berberoglu.
The decisions were announced in parliament after appeals courts upheld Berberoglu's conviction for disclosing government secrets and the convictions of Guven and Farisogullari for being members of a terrorist organisation.
HDP has long been accused of ties to the PKK, which in the last 30 years has killed more than 40,000 people, including women and children. Turkey, the US and the EU recognise the PKK as a terrorist organisation.
Given, from the southeastern Hakkari province, was sentenced to six years and three months in prison by a provincial court for "being a member of an armed terror group". The HDP denies such links.
Farisogullari, from the southeastern Diyarbakir province, received a nine-year sentence, also for "being a member of an armed terror group".
Berberoglu, an Istanbul lawmaker, was sentenced to five years and 10 months in prison for leaking state secrets to a newspaper in June 2017.
He was found guilty of leaking footage to a journalist showing National Intelligence Organisation trucks being stopped en route to Syria in January 2014. In that incident, gendarmerie officers affiliated with the Fetullah Terrorist Organisation (FETO) stopped the trucks on their way to Syria despite government orders to let them pass.
"This disregards the national will. We will continue the democratic fight to obtain justice, rights and law," CHP leader Kemal Kilicdaroglu wrote on Twitter.
The governing Justice and Development Party (AK Party) has 291 deputies in the 600-seat assembly, while the CHP now has 138 seats and the HDP has 58 seats.
FETO and its US-based leader Fetullah Gulen are known for attempting to infiltrate almost every organ of the state to destabilise the government.