One of the migrants, Meet Singh Kapoor, died in the overnight crossing from Belgium to Tilbury Docks last August.
Taha Sharif, 38, of High Cross Road, Tottenham, was convicted following a seven-week trial at Basildon Crown Court.
The jury is yet to reach a verdict on three other defendants, who are all from Northern Ireland.
Stephen McLaughlin, 34, of Limavady, Londonderry; Timothy Murphy 33, of Elmgrove, Londonderry; and Martin McGlinchey, 47, of Derryloughan Road, Coalisland, County Tyrone, deny conspiracy to facilitate illegal entry into the UK.
The container was discovered on 16 August last year when docks staff heard "screaming and banging" coming from inside, Essex Police said.
The group of Afghan Sikh migrants, which included 15 children, is believed to have fled Afghanistan after suffering persecution.
A man has been found guilty of attempting to smuggle 35 Afghan Sikhs into the UK in a shipping container.