The 33-year-old was presented by the club on Wednesday alongside club president Joan Laporta the day after Barcelona's 6-0 win over MLS club Inter Miami in a friendly that kicks off their tour of the United States.
"I'm very happy to be here," Lewandowski said at the presentation. "It was hard work to join Barcelona, but in the end I'm here. I know we have work to do, we have huge potential in the team, huge quality. I'm ready to be a part of this big club with an amazing history and make new history, with titles as well. I'm very happy."
"In the next training session I'll be on the pitch with the team and I'm ready to play in the next game [against Real Madrid]. Everything that happened in the last few days was amazing, it happened fast but that's football. You have to be ready for everything."
Lewandowski will sign a four-year contract with a release clause set at €500 million, Barcelona said in a statement. He had 12 months remaining on his Bayern contract and moved to Barcelona for €45m with a possible €5m in add-ons, the 26-time Spanish champions confirmed.
The Poland international has twice won the Golden Boot as Europe's leading goalscorer and finished as runner-up for the 2021 Ballon d'Or. He joins Pablo Torre, Franck Kessie, Andreas Christensen and Raphinha as additions as Barcelona look to build a squad to compete for LaLiga and the Champions League under coach Xavi Hernandez.
Oh, Robert ... we're excited, too 😉 pic.twitter.com/74HYaSOQ5d— FC Barcelona (@FCBarcelona) July 19, 2022
He was one of the club's top targets this summer and helped push through the move as he sought a new challenge after eight glittering years at Bayern Munich.
ESPN reported last month that Barca had made a series of bids -- the latest worth over €40 million -- for Lewandowski, who had just a year left on his contract, but were unable to convince Bayern until progress was finally made in talks.
He began his career in Poland, winning a league title with Lech Poznan. He joined Borussia Dortmund in 2010 and became one of Europe's most highly-rated forwards as he won two Bundesliga titles with Dortmund and reached the Champions League final before joining Bayern on a free transfer in 2014.
At Bayern, Lewandowski scored 344 goals in 375 appearances, placing him second on their all-time scorers list behind Gerd Muller.
He won the Bundesliga in all eight seasons at the club, as well as the Champions League in 2020, and was named Best FIFA Men's Player in 2020 and 2021.
Information from ESPN's Sam Marsden contributed to this report.