"It's not difficult to imagine what it was like with 42 people squashed into six square meters," presiding judge Xenia Krapfenbauer said, calling it an "atrocious case".
The Romanian defendant, 37, said that he did not know how many people were inside and that he had been paid €1,500 ($1,705) to drive the lorry.
By the time Austrian police stopped the vehicle in July near Vienna, the migrants had been locked up for seven hours non-stop, with temperatures outside more than 30C (86 Fahrenheit).
The migrants from Syria, Iraq and Afghanistan did "thank God" however have air, Krapfenbauer said at the trial in Korneuburg in eastern Austria.
Seventy-one migrants in another lorry found abandoned in Austria in August were not so lucky, suffocating in a case that German Chancellor Angela Merkel called a "warning" to Europe.
Austria is a major transit point for refugees entering from Hungary, on their way to Germany and elsewhere. Since the August tragedy, Austrian police have stepped up checks for people smugglers.