“It is a strong vote of confidence in our workforce and in Yeovil’s future,” he added.
Leonardo’s chief executive, Roberto Cingolani, earlier said the factory’s future would be at risk if it was not awarded the government contract.
The Yeovil factory was previously used to built planes used in World War One under the name Westland.
In the 1950s, it switched to making helicopters and more recently has specialised in Merlin and Wildcat helicopters.
Leonardo has sites in Edinburgh, Luton, Basildon, Bristol, Newcastle, Southampton and Lincoln, employing thousands more workers in its supply chains.