It was one of two Chinese companies trying to buy the assets of MG Rover, the other being Shanghai Automotive. MG Rover went into receivership in April.
"Nanjing will now begin to take control of the assets and develop its plans for the future," says Tony Lomas of PwC.
The news is a blow for the UK businessman David James, whose Kimber group had put in two bids to buy parts of Rover.
Joint administrator Lomas said Nanjing intended to relocate the engine plant and some car production plant to China but to "retain some car production in the UK".
He added that Nanjing, China's oldest carmaker, also planned to develop a research, development and technical facility in the UK.
#AM_ART_SPLIT# For a transitional period a workforce will continue to be employed by MG Rover Group and engine maker Powertrain.
They will assist the administrators as they have for the last three-and-a-half months, following the demise of Rover in early April when it ran out of money after a proposed tie-up with SAIC collapsed.
"In the meantime Nanjing intends to begin to hire staff to assist it in implementing and developing its strategy," Lomas said.
Nanjing had earlier said it wanted to restart car production in the West Midlands, but may look to use other sites as well as the former Rover site at Longbridge in Birmingham. Cars will be built under the MG marque and may include sports models and small and medium sized vehicles.
However, it also previously expressed plans to shift production of small and medium-sized cars to China, and then export kits to the UK for final assembly.
Nanjing has indicated before it plans to use MG as its main marque in Europe while developing other MG Rover brands, such as Austin, elsewhere.
Nanjing's successful bid could start a prolonged legal battle.
SAIC bought the intellectual property rights to sell the Rover 25 and 75 models in China during a previous attempt to take over the carmaker. Nanjing had previously rejected any claims that SAIC's ownership of the rights to the Rover 25 and 75 engines would affect its plans.
And Honda - which owned the rights to some of MG Rover's technology - has repossessed equipment and blueprints, making it more difficult for any buyer to restart production of the Rover 45 - based on the Honda Civic - or MG ZS models.