The premiership Eagle played 215 games for the club since being picked up with the third pick in the 2007 draft, and is now a life member of West Coast.
“I have had a wonderful time at the Eagles, the club I supported as a kid,” Masten told the club’s website.
“It was a dream to play for them and to play in a premiership last year was the ultimate for me.
“Over the last 12 or 13 years I have enjoyed every minute of it and have made some life-long friends. I will certainly miss the boys, we have a really special bond, but it is time to have a look at other options.”