Wigan came back from 16-2 down in Saturday's Grand Final, scoring 28 unanswered points to win the Super League for the second time during Tomkins's five years at the DW Stadium.
Tomkins, 24, will now leave Wigan to join the New Zealand Warriors for a world-record £700,000 fee.
"It's unbelievable, this is what we dreamt of," Tomkins told Sky Sports News at Old Trafford.
"There are a few of us leaving, we are a really tight group and the players spoke about a fairytale ending. This was it.
"We are a really tight group and we knew if we stuck to our game plan we would come back into it."
Tomkins scored 23 Super League tries during his final season in Lancashire.