The contract, worth $582.2 million, was awarded just days after Rolls-Royce sold its 50 percent stake in the RTM-322 program to Turbomeca of France.
Under the sales agreement, Rolls-Royce will transfer its operational tasks in the engine program over a multiyear period.
The ministry said the new contract simplifies the engine support supply chain, improves technical support and increases the availability of spare parts, and that it will also help to reduce the numbers of major repairs needed on airframes and lead to the government saving more than $475 million in costs.
"This contract will provide important support for our Merlin and Apache fleets, which play a vital role defending this country's interests around the world," said Minister for Defense Equipment, Support and Technology Philip Dunne. "This includes defending the U.K. and protecting our personnel on operations in Afghanistan.
"By improving the way we work with industry to maintain our helicopters with contracts like these, we can keep Apache and Merlin helicopters in the air for longer, which also ensures best value for money."