There were reports of interest from European clubs, including AC Milan, but the 37-year-old instead opted to make the switch to the USA.
And Lewandowski, who established himself as one of the most prolific goalscorers in European club football history during spells with Borussia Dortmund, Bayern Munich and Barca, admitted he needed a change.
"I decided that after Barcelona is over for me, I didn't want to stay in Europe," the striker said at his first press conference since signing for Chicago Fire.
"I didn't want to play anymore after Barcelona and a different club [in Europe]. From one side, of course, that was a difficult decision for me, for my family, to move outside of Europe.
"But from the other side, we know that we wanted to stay in a different club because of what we did in Barcelona. And I couldn't imagine myself in a new [European] club besides Barcelona."
Lewandowski enjoyed a trophy-laden period with Barcelona, winning three La Liga titles, a Copa del Rey and three Supercopas de Espana.
He scored 120 goals in 193 appearances across all competitions for the Blaugrana, earning the Pichichi Trophy as La Liga's top scorer in 2022/23.
Turning his attention to the next chapter in North America, Lewandowski said: "I see the potential to win titles with the new club. And I'm very, very happy because it's the new step in my career, the new step in my life.
"But I hope that we can enjoy a lot and also, we can do our job winning not only the games, but also the titles.
"And now we are in a good position, but of course we have to work hard and I hope that we can enjoy after the season what we achieve."
Chicago Fire sit third in the Eastern Conference table, with the MLS season set to resume after the World Cup in the USA.
Gregg Berhalter's side, who are seven points behind league leaders Nashville and five off Lionel Messi's Inter Miami, have made impressive progress this year.
And the hope is that Lewandowski can fire them to MLS success.
"This is a massive signing for our football club. We're excited to bring Robert to the club," Berhalter said. "We're excited to see how he can change the culture.
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'All going badly wrong' for Newcastle as Lewandowski joins the party
"One thing that I've got when I've gotten to know Robert, not only is an amazing soccer player, he's an amazing person, very humble person, very driven person.
"You don't play this long at this high of a level without being an absolute top professional. So we're excited to bring him to the club and really have his expertise and have his way of professionalism rub off on the rest of the team.
"We have a good team right now and we think Robert is a piece that can help take us to the top."
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