The veteran striker announced the news through a video posted on Instagram, where he reflected on some of his best moments in Barcelona colours. Lewandowski thanked the club, supporters and president Joan Laporta for what he described as one of the greatest chapters of his career.
"After four years full of challenges and hard work, it's time to move on," Lewandowski wrote. "I leave with the feeling that the mission is complete. Four seasons, three championships."
The Poland international also paid tribute to the Barcelona fans, saying the support he received from the first day at the club would never be forgotten.
"I will never forget the love I received from the fans from my very first days. Catalonia is my place on earth," he added.
Lewandowski arrived at Barcelona from Bayern Munich in 2022 and quickly became one of the key figures in the club's rebuilding project. During his time at Camp Nou, he helped Barcelona win three La Liga titles, a Copa del Rey and three Spanish Super Cups.
Despite turning 37 later this year, the striker remained an important player for Barcelona. He scored 119 goals and provided 24 assists in 191 appearances, numbers that underlined his impact during a period in which the club returned to competing for major honours.
Barcelona also released an emotional farewell message for the forward, thanking him for his contribution and describing him as "Culer forever."
Lewandowski is expected to say goodbye to supporters during Barcelona's final home game of the season against Real Betis on Sunday.
Attention will now turn to his next move, with clubs from Saudi Arabia and Major League Soccer in the United States reportedly interested in signing the experienced striker ahead of next season.