Gatwick CEO, Stewart Wingate, told Airport World that the decision was based purely on economics as UK-based ANS provided the best deal for the airport.
ANS says that today's transfer of operations is the culmination of a 14-month transition effort, the largest of its kind ever completed.
It will provide air traffic control and air traffic engineering services over a 10-year period at what is the world’s busiest single runway airport with a maximum of 55 aircraft movements per hour.
London Gatwick Airport is also Europe's leading airport for point-to-point flights serving more than 200 destinations in 90 countries and in 2015 the rolling total of passengers exceeded 40 million.
Managing director of ANS, Werner Spier, says: “The incredible effort from everyone involved in the transition resulted in a smooth and seamless handover of services.
"We are now looking forward to delivering high-quality services to Gatwick Airport and its customers in the coming years and providing the wider market with flexible, transparent and customer-centric air traffic control services.”
NATS will continue to provide approach control to Gatwick from its centre at Swanwick.
The company says: "We are very proud of our track record at Gatwick, which is, by a large margin, the busiest and most efficient single runway in the world and where NATS last summer delivered a record 934 movements in a single day.
"We have worked closely with ANS to ensure a safe and professional transition, including seconding 24 employees to support the operation for the next two years."