The TNRL was expelled from the International Rugby League (IRL) in March last year, after a long-running battle over governance, money and a threatened player boycott.
A two-day hearing was held in December, with CAS confirming on Tuesday the resolution of the IRL's Board to expel the TNRL from its membership had been upheld.
The panel of three arbitrators from the USA, Australia and Canada, concluded the expulsion was justified] after the "TNRL's refusal to cooperate with or to participate in the IRL's investigation and consultation processes."