More than 100 defendants are on trial on charges including trafficking, kidnapping and murder.
Facing severe repression in Myanmar, Muslim Rohingya have for years been fleeing the country, paying people smugglers to help them get out.
In 2015, thousands were left stranded at sea and abandoned in jungle camps.
The crisis escalated after international pressure forced the Thai authorities to crack down on the smuggling networks.
This led to the smugglers abandoning the refugees, leaving them on their sea and land routes with no neighbouring country willing to take them in.
The current trial was sparked by the discovery of mass graves of refugees in jungle camps near the Thai-Malaysian border.
Most of those indicted are from Thailand but several citizens of Myanmar (also called Burma) and Bangladesh are also being held.
Among the defendants is a high-ranking Thai military official, Lieutenant-General Manas Kongpan.
A senior policeman who led an investigation into human trafficking in Thailand, Major General Paween Pongsirin, fled to Australia fearing his life was in danger from influential figures implicated in trafficking in his country.
The Rohingya – a distinct Muslim ethnic group who are effectively stateless – have been fleeing Myanmar for decades with Thailand, Malaysia and Indonesia the most desired destinations.
While they say they are descendants of Arab traders who have been in the region for generations, Myanmar’s governments insist they are not a genuine ethnic group but rather Bengali migrants.
Among the refugees stranded during the 2015 crisis were also many economic migrants from neighbouring Bangladesh.