Lewandowski left Bayern Munich earlier this summer in a £42.
5m deal after scoring 344 goals in 375 games for the German champions.
The Catalan giants and the Polish international have agreed to a four-year contract that, according to Marca via The Mirror, has a €500 million (£431 million) release clause.
Lewandowski is expected to make €10 million (£8.6 million) in his first year in Spain, €13 million (£11.2 million) the following year, and €16 million (£13.8 million) the year after that.
The forward's salary will increase to €13 million (£11.2 million) for the fourth season of his contract, and Barcelona has the option to end it if he plays in fewer than 55% of the team's games in his third season.
Lewandowski, 34, will receive bonus payments if Barcelona wins the Champions League, a La Liga championship, or both of those honors as well as the Copa del Rey, according to other details of his contract that have been made public.
Lewandowski, who scored five goals in the first four La Liga games, has helped his new team start the season with three victories and a draw.
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