The latest format, which follows experiments with 40-, 50- and 60-over competitions, as well as four-day county championship matches and T20 contests, was presented to chairmen and chief executives of the county clubs and the MCC on Thursday.
It is due to launch in 2020.
"This is a fresh and exciting idea which will appeal to a younger audience and attract new fans to the game," ECB chief executive Tom Harrison said in a statement.
"Throughout its development, we have shown leadership, provided challenge and followed a process. We will continue to do that as the concept evolves.
"Our game has a history of innovation and we have a duty to look for future growth for the health and sustainability of the whole game."
The ECB members voted overwhelmingly in favour of a new city-based competition last year, with matches to be played in a five-week window in the middle of the summer.
Southampton, Birmingham, Leeds, London, Manchester, Cardiff and Nottingham have been selected as venues for the tournament, with Lord's and the Oval each playing host to a London-based team.
The tournament will feature aligned competitions for both men's and women's teams sharing a common format, brands and team identities.
(Reporting by Hardik Vyas in Bengaluru,; Editing by Neville Dalton)
