The Chinese carmaker, which owns the MG brand, hopes to build 700 units at the Birmingham factory by the end of the year.
Longbridge is the final assembly point for the TF, whose components are largely manufactured in China.
Its UK dealers are due to begin sales of the limited edition TF LE500 launch version next month.
Retailers were invited to Longbridge in mid-July to examine the car, which is priced £16,399. Only 500 units are being sold, before a wider range of TF variants goes on sale.