Fellaini left United to join Chinese club Shandong Luneng in a big-money deal on February 1.
He has now opted to call time on his Belgium career having won 87 caps and scored 18 goals since making his debut way back in 2007.
The 31-year-old posted an emotional message on Instagram announcing the end of his international career.
"After twelve years of representing Belgium at the highest level, I have decided to retire from senior international football," Fellaini said.
"It has not been an easy decision for me and not one I take lightly however I feel that the time is right for me to step down and allow the next generation of Belgian players to continue this very successful period in Belgian football history.
"It has been an honour to represent my country 87 times and to be a part of two World Cups and a European Championship campaign for Belgium."