Truck driver Maurice Robinson, 25, who is known as Mo, is due to appear at Chelmsford Magistrates' Court on Monday after he was charged with 39 counts of manslaughter, conspiracy to traffic people, conspiracy to assist unlawful immigration and money laundering.
Robinson, who is from Northern Ireland, was arrested shortly after the bodies of eight women and 31 men were found in the refrigerated trailer attached to his Scania cab in an industrial park in Grays in the early hours of Wednesday.
All of the victims have now been moved from the vehicle in Tilbury Docks to Broomfield Hospital in Chelmsford, for post-mortem examinations to be carried out.
But families face an agonising wait to find out if their loved ones were among the dead after Essex Police launched "the largest mass fatality victim identification process" in the force's history.
Officers initially believed they were all Chinese nationals, but a representative of VietHome - a website for Vietnamese people in the UK - said it has passed on the pictures of almost 20 people who have been reported missing to police.
Police said they are investigating a "wider conspiracy" after claims surfaced that the lorry could have been part of a convoy of three carrying around 100 people.
The mother and a sister of 19-year-old Bui Thi Nhung set up an alter in the village of Yen Thanh in north-central Vietnam after a family friend in the UK told them she had died after paying thousands of pounds in the hope of finding work in a nail bar.
Relatives of 26-year-old Pham Tra My told the BBC they have not been able to contact her since she sent a text on Tuesday night saying she was suffocating.
"I am really, really sorry, Mum and Dad, my trip to a foreign land has failed," she wrote.
"I am dying, I can't breathe. I love you very much Mum and Dad. I am sorry, Mother."
The woman's father, Pham Van Thin, told CNN: "The smugglers said that this was a ... safe route, that people would go by aeroplane, car... if I had known she would go by this route, I would not have let her go."
Another Vietnamese father, Nguyen Dinh Gia, fears his 20-year-old son, Nguyen Dinh Luong, was among the victims.
The Vietnamese Embassy in London has started a hotline while the ambassador to the UK, Tran Ngoc An, spoke to Home Secretary Priti Patel on Friday night before meeting investigators from the National Crime Agency and Essex Police.
Detective Chief Inspector Martin Pasmore told reporters on Saturday the ambassador had visited the civic centre in Grays to pay tribute to the victims.
He said there were "very, very few" identity documents recovered and that police will share fingerprints with Vietnamese authorities in a bid to identify the bodies.
Investigators will also look at tattoos, scars and belongings, including jewellery and clothing, with each of the victims said to have had some kind of bag.
More than 500 exhibits have been collected, including mobile phones, which will be downloaded and interrogated for any messages that could give clues to the identity of the victims or how they came to be in the back of the trailer.
Three other people arrested over the deaths remain in custody, while a man wanted in connection with the investigation was arrested at Dublin port on Saturday.
Gardai said the man, who is in his early 20s and from Northern Ireland, was held over an unrelated outstanding court order.
He is understood to be sought by Essex Police as part of their probe, and the force confirmed officers are in touch with Irish police.
A 48-year-old man, from Northern Ireland, was detained at Stansted Airport on Friday on suspicion of conspiracy to traffic people and manslaughter.
Officers had earlier arrested a couple named locally as haulage boss Thomas Maher and his wife Joanna, both 38, in Warrington, where they have a four-bedroom home.
The pair, originally from southern Ireland, were held on suspicion of 39 counts of manslaughter and people trafficking.
In Belgium, police are hunting the driver who delivered the trailer to Zeebrugge, the port it left before arriving in the UK.
It is not yet known when the victims entered the trailer, where temperatures can be as low as minus 25C if the fridge is activated, or the exact route it travelled.
Belgian officials said the trailer arrived at Zeebrugge at 2.49pm on Tuesday and left the port the same day en route to Purfleet.
The trailer arrived at Purfleet at around 12.30am on Wednesday, and was picked up by the cab, known as the tractor, which arrived from Northern Ireland via Holyhead in North Wales on Sunday.
The lorry left the port at Purfleet shortly after 1.05am before police were called to the Waterglade Industrial Park on Eastern Avenue in Grays at 1.40am.