The pair are being joined by Pascale Reed, who quit as the McCann planning chief in May, and Michelle Katz, previously the new-business director of the Red Cell agency in London.
The fledgling operation will be called David, reflecting what its founders claim will be its philosophy of providing business solutions to help prospective clients "kill giant problems".
Their agency opens its doors with two pieces of business. One is Lyle & Scott, the knitwear manufacturer traditionally associated with golf but which is seeking to turn itself into a fashion brand.
The other is Everyman, the cancer charity and a former Red Cell client.
Two other pieces of business, including a courier service, are to be announced.
The partners, equal equity holders in the venture, are currently looking for a managing director to take day-to-day charge of the agency born nine months after Frank and Katz were axed from the WPP-owned operation.
The move was seen as a "deck-clearing operation in advance of an acquisition.
"It's very difficult to walk away from a highly paid job to start an agency, Frank commented. "But if the job walks away from you and you leave with a large amount of money it becomes considerably easier."
The start-up revives some previous working relationships, including that of Frank and Le Blond, who were trainees at Ogilvy & Mather and worked together on O&M's Bupa and American Express accounts.
Le Blond, whose agency career includes spells at D'Arcy and Bates UK, also worked with Reed at McCann before leaving 18 months ago to become a commercials director. He will continue to take on directing assignments through Garretts.