Ronaldo played 234 times for Portugal and scored 146 goals - a world record.
But the forward's powers have been waning in recent years and he fell out with national coach Jorge Jesus last month after Jesus refused to play him in a Nations League match.
Ronaldo immediately left the team camp and was handed a 30-day suspension.
Although it was rumoured that he intended to return to the international fold, on Thursday the five-time winner of the Ballon d'Or released a video on his Instagram account in which he said he was ending his international career.
"To the Portuguese people, the day has come for me to hand back the number seven shirt of our national team," Ronaldo said.
"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.
"Today the time has come to pass it on to the future. It was not an easy decision, because some decisions are not made with the mind alone - they are also made with the heart.
"A journey that began in August 2003 and changed my life forever has come to an end."
In the highlight of his international career, Ronaldo won the European Championship with Portugal in 2016 in France, although he had to leave the field during the final with an injury.
At this year's World Cup in the United States, Canada and Mexico, he scored three goals but Portugal were knocked out in the Round of 16 by eventual winners Spain.