The trial took place in Hungary, which took over the proceedings from Vienna after it emerged that the migrants had suffocated in Hungary.
Ten other suspects were also found guilty and handed prison sentences of between three and 12 years by the court in the southern town of Kecskemet.
The men had been charged with “aggravated murder with particular cruelty” in the year-long trial, which put the spotlight on the plight of migrants who put their lives into the hands of human traffickers.
The victims - 59 men, eight women and four children, including a baby - came from Syria, Iraq and Afghanistan.
Having made their way to the Serbian border with Hungary, they were packed into an air-tight poultry refrigerator truck, their cries to stop and open the doors for fresh air ignored.
Realising what had happened, the driver abandoned the refrigerated lorry by the side of a motorway in Austria.
When Austrian police opened the back of the lorry, they found the bodies piled on top of each other. Investigations showed they had been dead for two days, suffocating shortly after being picked up in Hungary, then a key transit country on the Balkan migrant trail.
The group had been part of hundreds of thousands of desperate people fleeing war and misery in the Middle East and elsewhere in 2015, triggering Europe’s worst migrant crisis since World War II.
The deaths led a shocked German Chancellor Angela Merkel to announce she would open her country’s doors, eventually allowing in more than one million refugees, mostly from Syria.
Hungarian officials said the Budapest-based ring was a professional network with more than 15 vehicles used to transport refugees who were trekking up from Greece along the western Balkans to Europe.
The gang had smuggled more than 1,100 people from Hungary into Austria since February 2015, charging up to 1,500 euros ($1,760) a head.
State prosecutor Gabor Schmidt had asked for life terms for the main four accused, insisting that three should get life without parole under Hungarian law.
