The 35-year-old German driver shared the news in a poetic video on Instagram ... saying, "At the end of the year, I want to take some more time to reflect on what I will focus on next. It is very clear to me that, being a father, I want to spend more time with my family."

"But, today is not about saying goodbye. Rather, it is about saying thank you -- to everyone -- not least to the fans, without whose passionate support Formula 1 could not exist."

Vettel won four-straight championships with Red Bull from 2010-13 ... and has also suited up for Toro Rosso, Ferrari, and most recently Aston Martin -- securing 53 career wins over 15 seasons.

There had been much speculation about the driver's future, as his contract is up at the end of 2022. Now, the talk can be put to rest.

"Committing to my passion the way I did and the way I think it is right, does no longer go side by side with my wish to be a great father and husband," Vettel added. "The energy it takes to become one with the car and the team, to chase perfection takes focus and commitment."

"My goals have shifted from winning races and fighting for championships to seeing my children grow, passing on my values, helping them up when they fall, listening to them when they need me."

The announcement was Vettel's first-ever social media post ... and the whole thing is powerful.