Speaking on the BBC's Today programme, James said he would submit the offer once his financial backers have signed up.
James hopes to resurrect Rover as a niche car manufacturer.
Seperate bids have already come from Chinese carmakers Shanghai Automotive Industry Corporation (SAIC) and Nanjing Automobile Corporation.
James's offer for Rover will depend on him finding a buyer for the company's Powertrain engine-making division.
Administrator PricewaterhouseCoopers (PwC) is said to have valued Rover and Powertrain at more than £50m.
PwC is expected to give its decision on the sale within a week.