The deal with the French utility, which covers the Hunterston B power station in Ayshire and the Torness plant in East Lothian, will be worth £70 million annually to Doosan Babcock.
Some 1000 people are expected to be employed on the contract at any one time, including an unspecified number at Korean-owned Doosan Babcock's manufacturing site and headquarters in Renfrew.
Cameron Gilmour, Doosan Babcock's nuclear service director said the agreement with EDF would give the company access to a range of specialist skills and technologies that would support its UK power generation strategy.
Doosan Babcock said the agreement would continue until the last of the seven Advanced Gas Cooled Reactor stations ceased power generation.
Earlier this month EDF said: "Based on the expected life extensions, all seven of our AGR stations will be operating in 2023."
It hopes all seven plants will operate beyond 2023.
Opened in 1976, Hunterston B was originally due for closure in 2011. The life was first extended to 2016. In 2012 EDF extended that to 2023.
Torness came online in 1988, scheduled for closure in 2023. The agreement also covers the Dungeness B, Hinkley Point B, Hartlepool, Heysham 1 and Heysham 2 sites south of the border.
Doosan Babcock employs over 750 people at Renfrew.