The 41-year-old said that he would 'hand back the number 7 shirt' after the November international break.
"To the Portuguese people, the day has come for me to hand back the number seven shirt of our national team," Ronaldo said in a video on his Instagram account.
"I never felt it belonged to me alone, but for 23 years I had the privilege and the responsibility of wearing it, defending it and carrying it with me into stadiums all around the world," he continued.
Ronaldo has made 234 appearances for Portugal and scored 146 goals.
He holds the all-time record for international appearances and for international goals.
"Today I finish my walk on the pitch with the national team. I leave with my head held high, with pride in the path I took, and with the awareness that I gave everything I had for Portugal," he said.
"The goals pass, the cups are in museums, the records end up being beaten. But there is something that time can never erase, the place we occupy in people’s hearts.
"I spent my life working to be the best player in the world. Today I realise that the greatest victory was to have deserved to represent the best country in the world.
"Thank you for these 23 years. Thank you for having believed in me.
"Portugal will always be in me. Forever."