Selahattin Demirtas, co-chairman of the pro-Kurdish Peoples' Democratic Party (HDP), is in jail in Edirne in northwest Turkey but his hearing was being held in Ankara.
Demirtas and the party's former co-leader, Figen Yuksekdag, have been imprisoned with nine other HDP lawmakers on accusations of links to Kurdish separatists.
They were first detained in November, causing alarm in Europe and concern over the use of the state of emergency put in place after last year's failed coup.
There are multiple cases against Demirtas. In this case, he is accused of "public humiliation of the Turkish government, the judiciary, the military or law enforcement agency". The charge is based on one of his social media postings, the HDP said.
Demirtas hit back at the proposal to handcuff him as "illegal and immoral" saying he was a lawmaker who represented "the will of people".
"As I did not accept wearing handcuffs, I was brought back to my cell around 4am (0300 GMT)," he said in a statement shared by the HDP.
Tight security
The Ankara courthouse was surrounded by riot police and even court personnel faced difficulties entering the building. Police told media they were not allowed to attend the hearing but some made it inside.
Lawyers taking part in the trial left the hearing in protest at the way it was being conducted, an AFP correspondent said.
Yuksekdag appeared in court for the first time on Tuesday on charges of disseminating "terror propaganda" for the outlawed Kurdistan Workers' Party (PKK).
Over 40,000 people have killed during the PKK's insurgency against the Turkish state since 1984.
The Council of Europe's human rights commissioner, Nils Muiznieks, meanwhile urged Turkey to immediately release ten human rights activists arrested Wednesday in Istanbul during a workshop.
"I call on the Turkish authorities to immediately release those detained... and strongly urge them to stop all arbitrary interferences with the legitimate work of civil society ," Muiznieks tweeted.
Among those detained are Idil Eser, Amnesty International's Turkey director, as well as one Swedish and one German national, both trainers.
They are accused of belonging to an armed "terrorist organisation," according to Amnesty's Turkey researcher Andrew Gardner.
Turkey frequently uses the phrase "terrorist organisation" to refer to supporters of US-based cleric Fethullah Gulen, who Ankara accuses of orchestrating last year's failed coup, as well as Kurdish separatists.
Amnesty had Thursday denounced the arrests, less than a month after Ankara remanded Amnesty's Turkey chair, Taner Kilic, in custody on what the group described as "baseless charges" of links to Gulen.
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