The Camp Nou club generated €840.8m during the 2018-2019 season, seeing them topple bitter rivals Real Madrid at the top of Deloitte's table.
Barca finished ahead of Madrid by some distance, with Los Blancos bringing in €757.3m across the course of the campaign, though that was enough to keep them second and in front of Manchester United.
The Red Devils may have underwhelmed on the pitch in recent seasons, but they remain a major financial power, with revenues reaching €711.5m.
United are one of eight Premier League clubs in the top 20, with Manchester City (fifth), Liverpool (seventh), Tottenham (eighth), Chelsea (ninth), Arsenal (11th), West Ham (18th) and Everton (19th) joining them.
However, United could potentially slip next year due to a lack of Champions League action this term, with Bayern Munich (€660.1m) and Paris Saint-Germain (€635.9m) the biggest threats to knocking them out of the top three.
Deloitte also understand United is at risk of losing its status as the Premier League's highest revenue-generating club for the first time next year, with City and Liverpool very much on the rise.
Napoli and Lyon are the only new entrants to the top 20.