The operator acquired Ladbrokes Coral in March 2018 and the latest move finishes the migration of all its purchased brands, including Ladbrokes, Coral, Gala Bingo, Gala Casino and Gala Spins.
GVC said this was the largest transfer the operator has completed, which was carried out on time and on budget.
The migration sees 25 million Ladbrokes Coral customer accounts being moved across to the GVC proprietary platform, including 12.5 million just from Ladbrokes.
GVC is still on track to deliver £130m ($157.7m) of annualised synergies by late 2021 and has hinted at further M & A activity in the future following the migration.
GVC COO Shay Segev said: "The GVC integration model has proved itself time and again to be extremely effective at integrating large-scale operations with minimal disruption to our underlying business.
"As a result, we are confident in our ability to take advantage of the attractive M & A opportunities we believe will present themselves to us in the future, while further boosting the growth of our existing business."
In March, GVC reported a 2% year-on-year rise in 2019 pro forma group net gaming revenue (NGR), to £3.66bn ($4.43bn), while NGR rose by 1% for Q1 2020.
