Fellaini started his professional career with Standard Liege, making 84 appearances for the Belgian side, before making the move to English football with Everton in 2008.
The midfielder scored 33 goals and registered 26 assists in 177 appearances for the Toffees before making the move to Man United in the summer of 2013.
Fellaini also made 177 outings for the 20-time English champions, scoring 22 goals and registering 12 assists, winning the FA Cup, EFL Cup, Community Shield and Europa League, before leaving for China.
The 87-time Belgium international played for Shandong Taishan between 2019 and 2023, departing the Chinese outfit at the end of the season, he has now announced his retirement from professional football.
"I am writing this post to announce that after a career of 18 years, I am retiring from professional football," Fellaini posted on his official Instagram account.
"But it all started long before these 18 years. I remember, like the day of yesterday, my first game as a child, the endless training sessions with my dad, my first selection for Standard de Liege, and my first selection for the Belgian national team. Time flies!
"What an incredible journey it has been! I am so grateful to have played the sport I love at the highest level. I am proud to have represented Standard in Belgium, Everton and Manchester United in the UK, and Shandong Taishan in China.
"It was an honor to have played for the Belgian national team at the Olympics of 2008, Euro 2016 and the World Cups of 2014 and 2018.
"I have played in front of the best fans in the world, and I want to take this moment to thank all of them for their unwavering support throughout my career. Your encouragement and passion have been a constant source of inspiration for me.
"All of this would have been impossible without my family, teammates, coaches, advisers and everyone who has been a part of my journey. Your love, guidance, support, and friendship have been invaluable. Thank you!
"As I embark on this new chapter in my life, I look forward to new challenges, but be assured, I will continue to support the beautiful game in any way I can. See you soon!"
Fellaini managed 50 goals and 13 assists in 141 appearances for Shandong Taishan, winning the Chinese Super League in 2021 and Chinese FA Cup in 2020, 2021 and 2022, while he was a part of the Belgium squad that finished third at the 2018 World Cup.