Maker Hasbro said the cat received 31% of a Facebook vote, trumping the robot, guitar, helicopter and diamond ring.
The iron took just 8% of the vote after it was neck and neck for elimination with the wheelbarrow and boot, meaning production of the token will cease.
The latest changes mark the first time fans have had a say on which token to add and which to replace.
Hasbro said people from more than 120 countries voted in the contest, sparked by chatter on Facebook where the game has more than 10 million fans.
The US firm will begin to replace the iron with the cat token on production lines immediately, with the updated game expected in stores later this year.
Eric Nyman, senior vice-president of Hasbro, said: "Cat lovers around the world will be happy to welcome the new cat token.
"While we're a bit sad to see the iron go, the cat token is a fantastic choice by the fans and we have no doubt it will become just as iconic as the original tokens."
The other tokens remain the car, Scottie dog, thimble, top hat and battleship.