23-year-old Quentin Deranque died after being assaulted by at least six people in connection with a French far-right protest in Lyon.
The man who has now been arrested is suspected of having a direct connection to the violence, and his partner is suspected of helping him escape.
Six of those previously arrested are suspected of having participated in the assault.
On Wednesday, the headquarters of the left-wing party La France Insoumise in Paris was evacuated after a bomb threat. Shortly afterwards, the threat was declared over.
It was initially unclear whether the threat was directly related to the fatal assault.
