Their cases have heightened concerns of an authoritarian turn under Turkish President Recep Tayyip Erdogan.
Ten of the activists, including Amnesty's Turkey director Idil Eser, German national Peter Steudtner and Swede Ali Gharavi, were arrested while attending a digital security training workshop in July. They face prison sentences of up to 15 years, if found guilty.
The activists have been charged with plotting an uprising and aiding Kurdish and left-wing militants. They also stand accused of abetting the movement led by a US-based cleric the Turkish government blames for a 2016 coup attempt.
"I dedicated my life to truth and justice, and that is all I ask of this court," Ozlem Dalkiran of the Citizens' Assembly organisation testified, according to Amnesty's International Director for Europe John Dalhuisen.
Also Read
Human rights groups say the defendants are accused of "trumped up" charges.
Amnesty Turkey chairman Taner Kilic, who was imprisoned in June, is appearing before a different court for alleged links to cleric Fethullah Gulen. He is accused of using an encrypted mobile messaging application allegedly employed by Gulen's network.
"At the very least, our expectation and our hope is that they will be released from prison."
Gardner added: "It's been a very difficult situation for all human rights organisationsin Turkey for some time. But for 11 human rights defenders to be . picked up after a routine human rights seminar is an escalation of repression in Turkey."
The trial is one of several cases that have deepened a rift between Turkey and European nations, notably Germany, which considers Steudtner and some 10 other German or German- Turkish citizens jailed in Turkey to be political prisoners.
His jailing prompted the German government to toughen its stance toward Turkey by revising its travel advice and threatening to withhold backing for investments there.
"Turkey always points to the independence of its judiciary -- we respect that, and against this background we hope that today's proceedings in Istanbul will send an encouraging signal of the rule of law and judicial independence in the case of Peter Steudtner," Foreign Ministry spokeswoman Maria Adebahr said in Berlin.
Turkey has arrested more than 50,000 people since the failed coup and sacked at least 110,000 others from government jobs.
The crackdown was initially launched to deal with alleged coup-plotters, but expanded to include other government opponents, such as academics, journalists and legislators, critics say.
"These two trials will be an acid test for the Turkish justice system and will demonstrate whether standing up for human rights has now become a crime in Turkey," Amnesty's Dalhuisen said.
Disclaimer: No Business Standard Journalist was involved in creation of this content