Northern Ireland lorry driver Maurice Robinson, 25, who is accused over the deaths of 39 migrants, has pleaded guilty at the Old Bailey to plotting to assist illegal immigration.
Robinson, who was allegedly part of a global smuggling ring, is charged with the manslaughter of a group of men, women and children found dead in a refrigerated trailer.
The bodies of eight females and 31 males were discovered in the trailer attached to his Scania cab in an industrial park in Grays, Essex, early on October 23.
The victims were later identified as coming from various provinces of Vietnam, with the youngest being two boys aged 15.
Robinson, who is known as Mo, appeared at the Old Bailey via video link from Belmarsh prison for a plea hearing.
Wearing a light blue sweater and tan trousers, he spoke to confirm his identity and British nationality.
During the hearing before Mr Justice Edis, he admitted conspiracy to assist unlawful immigration between May 1 2018 and October 24 2019.
The charge states that he plotted with others to do "an act or series of acts which facilitated the commission of a breach of immigration law by various persons".
He also admitted acquiring criminal property - namely cash - on the same dates.
The defendant, of Laurel Drive in Craigavon in Northern Ireland, was not asked to enter pleas to other charges, including 39 counts of manslaughter.
He is charged with conspiracy to commit human trafficking offences between May 1 2018 and October 24 2019.
The details of that charge state that he "arranged or facilitated the travel of other persons into the UK with a view to their being exploited".
He is also charged with transferring criminal property.
The defendant was remanded into custody until a further hearing on December 13.