Tigers say they are “pleased” the dispute with Solomona, rugby union club Sale and agent Andrew Clark has been settled.
The case had been due to go to trial later this year, but Tigers say the “litigation is concluded” following a joint offer made by the defendants.
Solomona joined Sale last year, saying he had retired from rugby league, despite being contracted to Castleford until the end of 2018.
A statement from Tigers said: “Castleford Tigers believe the correct decision was made to bring this matter to a conclusion now.
“It not only means they are in pocket for a substantial sum of money, but the case has clearly proved that it is impermissible for a player to walk out on his contract without suffering a harsh financial penalty.”
The Rugby Football League described the case as “a matter of profound importance for sport” and praised Castleford for their “dignity, integrity and tenacity”.
RFL chief executive Nigel Wood, said: “They have done the whole of sport a great service.
“It is incredibly regrettable that this situation ever arose and we believe that national governing bodies from all sports and leagues must work together to ensure that clubs and players are protected and contracts are respected by all concerned.”