The Atletico Madrid defender, 31, made his senior team debut for Spain in 2020 and was part of the squad that beat Argentina 1-0 to win the World Cup in July, although he remained on the bench in the final.
"I realise that I’m still young and that, perhaps, if I continued to perform well, I’d still have years left to play in this jersey," Llorente wrote on Instagram.
"I know many of you won’t understand this, and I probably wouldn’t have understood it either if I were looking at it from the outside. But it’s a personal decision - one I’ve thought through very carefully and, above all, one that comes from the heart."
The former Real Madrid player thanked his teammates and reflected on Spain's triumphant World Cup campaign.
"I’ll cherish everything I’ve experienced, but above all, these last 52 days," Llorente said.
"With a wonderful group that fought until the very end to put Spain at the top. And that’s exactly what they did."