The 33-year-old will finish up at the end of the season, almost certainly to be Richmond's round-24 game against Port Adelaide.
After being drafted with pick two in the 2007 draft, Cotchin has played 305 games for Richmond - the fourth most in the club's proud history.
"I found my life purpose at Richmond," Cotchin said on Thursday.
"I look to the future with nothing but excitement, adventure, and opportunity, because of what I found here at Richmond and what Richmond people taught me.
"Finding out that creating an environment to help others realise and fulfil their potential not only inspired me but helped me to overcome my own fears.
"I have always given my best and left no stone unturned, in my dad's words - I have strived to make every post a winner."
Cotchin became Richmond captain ahead of the 2013 season, aged just 22.
He would go on to lead the Tigers to their first premiership in 37 years, the 2017 grand final victory over Adelaide.
Cotchin would certify himself as a Richmond immortal when he skippered the Tigers to more flags in 2019 and 2020.
He handed over the captaincy to Dylan Grimes and Toby Nankervis ahead of the 2022 season.
"Obviously Trent has achieved so much as a player, however, it is the power and impact of his leadership that has impressed me the most," Richmond chief executive Brendon Gale said.
Cotchin was jointly awarded the 2012 Brownlow Medal with Sam Mitchell after original winner Jobe Watson gave up the honour in 2016 due to Essendon's supplements saga.
The classy midfielder might not be the only Richmond great to bow out before the end of the season, with doubt hanging over the career of fellow veteran Jack Riewoldt.
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