The four-time Premiership star and one-time Brownlow Medalist announced his decision on Wednesday. 

Mitchell, who moved to West Coast in 2017 after a 15-year career with Hawthorn, said one year more would be "one too many". 

The 34-year-old will instead focus on coaching, moving into an assistant role with the Eagles from next season. 

"It's time for me to hang up the size nines. It's been a brilliant journey," Mitchell said at his press conference on Wednesday.

"The passion for completing my coaching work on a Monday morning has outgrown my passion to complete my recovery."

Mitchell said he wanted to announce his retirement now so that friends and family could attend the Eagles' fixture in Melbourne this weekend. 

"It's our last fixtured game in Melbourne this year so that's the reason for calling it now," he said.

However, Mitchell is still confident the Eagles can make the finals in 2017. 

"There's not just four weeks left in my eyes, there's a lot more football left in this group for this year," he said.