Steelmaker Jingye plans to invest £1.2bn at the main Scunthorpe works and on Teesside.
About 3,200 staff have been offered contracts, while 400 will be made redundant when the sale closes.
A further 75 jobs will transfer to Barrett Steel following the sale of four British Steel distribution centres, which will be integrated into the stockholder’s network of depots.
The purchase deal with administrators includes British Steel’s steelworks at Scunthorpe and UK mills at Teesside Beam Mill and Skinningrove, as well as subsidiary businesses FN Steel in the Netherlands and TSP Engineering.
It does not include British Steel’s French operations at Hayange, the acquisition of which is still subject to further negotiations with the relevant authorities in France and is hoped to be concluded separately.
Jingye’s investment plans include building an electric arc furnace on Teesside to makes products from recycled steel, building a 250MW power plant for the Scunthorpe factory which will be a third more efficient.
It also plans to build a new line for steel rebar and enhance the present rail mill.
Jingye Group CEO, Li Huiming, said: “It has not been an easy journey since we first announced our intentions in November but the longer I have spent in Scunthorpe, the more I have come to believe in the successful future of these steelworks and the employees that have made them famous throughout the world.
“Together, we can forge a new partnership that will mark the beginning of a new illustrious chapter in the history of British steelmaking.”