German group RWE is buying for plant for £105mln, which was its valuation at the end of last year.
The plant was mothballed in 2012 but recently had a new gas turbine installed.
Centrica said the sale was part of its asset disposal programme to reduce debt and re-focus on becoming a supplier rather generator.
The group’s majority stake in its oil and gas exploration arm Spirit and its minority stake in UK Nuclear are also up for sale.
King’s Lynn can produce enough power for all the 400,000 homes in Norfolk and comes with a 15-year contract to back up renewable energy sources.
Tom Glover, Country Chair for RWE in the UK, said the power station is a highly flexible and efficient combined cycle power plant that takes its UK gas-fuelled generating portfolio to 7.2 gigawatts in total.