Barca announced on Wednesday that they have secured the signing of Vitor Roque from Paranaense.
The Brazilian striker will join the LaLiga champions in the 2024-25 season and stay until 2031.
The deal is worth 40 million euros ($44.07 million) with another 21 million in bonuses, according to media reports.
The 18-year-old, who scored 22 goals in 66 games for Paranaense and helped them reach the Copa Libertadores final last season, is seen as the heir to Lewandowski who will be 35 next month.
He made his Brazil debut in March, becoming the youngest ever player to represent the five-time world champions.
“In footballing terms, a centre forward still in development but his adaptability means he can also play on the wing should the situation require,” Barcelona said in a statement.
“An excellent reader of the game he also stands out for his pace and his finishing skills in front of goal.”
Barcelona said they have inserted a buyout clause of 500 million euros into his contract.