After two incidents with small boats in the English Channel, the groups were rescued by RNLI in dark conditions.
According to French authorities, the 20-year-old Sudanese man was found unconscious on Friday and pulled out of the water after going overboard while trying to reach the UK along with others.
The man was taken back to shore, but was pronounced dead.
An investigation into the premeditated murder has begun, prosecutor Boulogne-sur-Mer said.
In the incident, a total of 32 people were rescued in front of Berck, near Calais, in a state of hypothermia, authorities said.
The death came less than two months later at least 27 people died when their boat sank off the French coast in November.
In 2022, after a record 2021, more than 450 people set out on a life-threatening voyage across the English Channel in small boats.
At least 271 people aboard 10 small boats arrived in the UK on Thursday, including a small child wrapped in an orange life jacket and wearing a hat.