Joseph and Donnacha O'Brien will work together as one of 12 teams in the Racing League competition which launches next summer.
The new initiative will see teams compete across 36 races - with each event worth £50,000 and total prize-money of £1.8million - over six weeks at Newcastle, Doncaster, Lingfield and Windsor.
The O'Briens will form the Irish team, with Tim Easterby and Richard Fahey representing the north while Charlie Fellowes, Hugo Palmer and George Scott are combining to form the first Newmarket-based squad.
There are three teams in the south, comprising of Andrew Balding and Richard Hannon as one side, George Baker, David Menuisier, Gary Moore and Amanda Perrett as another, with Wiltshire-based trainers, Roger Charlton, Alan King, Martyn Meade and Brian Meehan also banding together.
Six teams are still to be announced, with each outfit nominating 30 horses and three jockeys, plus a team manager who will decide on a selection for each race.
Oli Harris, Racing League's chief marketing officer, said: "We're thrilled by the broad range of support from trainers. We will shortly confirm the remaining six teams followed by details of the jockeys chosen to represent each team."
In a change to previously stated rules, and with regard for the British Horsracing Authority's review of the current whip rules which due to be published next year, the competition will no longer be a 'hands and heels' event in 2021.