On Friday afternoon, an official club announcement confirmed NUFC participation for the coming season.
Additionally, no more than two of the players over 21 can have made more than 40 first-team appearances, also as of June 30.
Liverpool will enter an U21 team to compete for the EFL Trophy for the first time in 2019/20 season, giving promising talents much-needed competitive action.
Newcastle's Under-21s, backed by 2,780 travelling fans, were beaten 4-0 by at the Stadium of Light in January.
The Blues saw off both Arsenal and Spurs' youngsters on their way to Checkatrade Trophy final glory against Sunderland at Wembley last season.
The Red Devils will enter a team comprised largely of Under-21 players as they make their debut in the competition.
The Magpies will take part in the competition for a third consecutive season, having first featured in the revamped cup competition in 2017/18.
The EFL Trophy continues to grow and we are delighted to welcome Liverpool and Manchester United U21s to the competition.
The draw for the group stage will take place in July with the first round of fixtures scheduled to take place week in the first week of September.