The Chinese manufacturer, which bought MG Rover after it collapsed almost a year ago, said Longbridge would have a renewed annual capacity of 15,000 cars. It will sell them in the UK and throughout Europe.
There are 80 people currently working at Longbridge, but Nanjing chief, YU Jianwei, said more could be taken on in the future.
"Car enthusiasts all over the world can be reassured that MG, one of the great motoring brands, is safe in our hands," he said.
"We are committed to re-building the marque in major markets, with cars supplied from the UK or China, as appropriate."