The German is making a shock move back to Manchester City, a year after leaving.
Gundogan will be allowed to depart Barca for free, despite having time left on his contract.
It has been a busy time for the midfielder, who also quit Germany duty this summer.
"After a few weeks of consideration, I have come to the conclusion that it is time to end my national team career," Gundogan explained in a social media post.
"I look back with great pride on 82 national games for my home country - a number I could never have dreamed of when I made my debut for the National A team in 2011.
“My highlight was clearly the huge honor that I was allowed to lead the team as captain at our home European Championship last summer! After all those years before, we have finally managed to make the nation proud again - that I was able to contribute a part of that makes me very happy.
"But already before the tournament, I felt a certain type of fatigue in my body, but also in my head, which made me think. And the matches at club and national level are not getting any less."