Victims included women and children desperate for a better life when they paid up to £14,000 each for a “VIP” smuggling service.
They were crammed into a lorry container shipped from Zeebrugge to Purfleet, Essex, in sweltering heat in 2019.
The Old Bailey heard how they desperately tried to raise the alarm as they ran out of air.
The migrants, two aged just 15, were found dead by lorry driver Maurice Robinson in Grays, Essex.
Robinson, 26, of Craigavon, and gang leader Ronan Hughes, 41, of Armagh, Northern Ireland, admitted plotting to people smuggle and 39 counts of manslaughter.
Romanian fixer Gheorghe Nica, 43, of Basildon, Essex, and Eamonn Harrison, 24, of County Down, who collected the victims, denied offences but were convicted by a jury.
Robinson, who also admitted money laundering, was jailed for 13 years and four months, Hughes was sentenced to 20 years, Nica to 27 years and Harrison to 18 years.