Talks between the club and player's management reached a final stalemate on Monday, with the Tigers unwilling to grant Marshall the lucrative contract extension he sought.
The 28-year-old's request for a release needs to be ratified by the Wests Tigers board but that appears to be a formality.
Marshall will see out the rest of the NRL season before embarking on the next chapter of his career, which is likely to be in the Super Rugby competition with either the Blues or the NSW Waratahs.
It leaves a big question mark over his availability for the Kiwis in their defence of the Rugby League World Cup in the United Kingdom this autumn.
If he joins the Blues, Marshall could have a crack at playing for the All Blacks in the 2015 World Cup being staged in England.
Marshall has played 193 matches for Wests Tigers and is their all-time leading points scorer.
"We are extremely disappointed to receive the news as we believe that we have been exceptionally generous to a player that has given us wonderful service over a number of years," said Wests Tigers chief operating officer Grant Mayer in a statement.
"Benji has obviously made a decision that he believes is right for himself and his family. All we can do is thank him wholeheartedly for what he has done for not only the club but the game as a whole.
"Benji Marshall in the eyes of all Wests Tigers supporters is a superstar and we have no doubt he will continue to support the club from afar."
Blues coach John Kirwan has previously held talks with Marshall's manager Martin Tauber, while Waratahs coach Michael Cheika will now be sounded out.
Japanese and French rugby union appear Marshall's next best options after Super Rugby, with a stint in the English Super League appearing unlikely at this stage.
- Sports & Recreation
- Wests Tigers
- Benji Marshall