The deal was undertaken by ComfortDelGro's wholly owned subsidiary in the UK CityFleet Networks.
ComfortDelGro's managing director and group CEO Yang Ban Seng said the acquisition will "enable the Group to grow and strengthen its position as the leading taxi circuit operator in London through an expansion of the customer and driver base".
Radio taxi circuits are operators of a door-to-door transportation service that uses London's black cabs.
Currently, ComfortDelGro is the largest taxi circuit operator in London with around 1,900 London taxis. The acquisition will add about 1,100 black cabs to bring the total fleet to 3,000.
Mr Yang also added that London Councils and Transport for London recently awarded CityFleet the Taxicard and Dial-A-Ride contract for another three years, with an option for a fourth.
Taxicard is the largest public sector day-to-day transport service in London for passengers with serious mobility impairments or who are severely sight impaired.
CityFleet has held this contract over several decades through its taxi subsidiary Computer Cab.