Brentford did not disclose the exact figure but said it surpasses the £42.5m paid to sign Dango Ouattara from Bournemouth last summer, making the 24-year-old the most expensive addition in the club's history.
Sangare signs a five-year contract with a club option for a further year, arriving off the back of an outstanding debut campaign in France in which he helped Lens finish second in Ligue 1 and win the Coupe de France for the first time in the club's history, starting the final as Lens beat Nice 3-1.
Across 33 appearances in all competitions for Lens last season, Sangare found the net three times and set up as many again, while leading every midfielder in the division for ball recoveries with 207 and ranking second for both tackles and duels won. That level of output earned him a place in the UNFP Ligue 1 Team of the Year and the Prix Marc-Vivien Foe, awarded annually to the best African player in the French top flight.
Bees manager Keith Andrews said the club had been tracking Sangare for some time.
"Mamadou is someone that we've tracked for quite some time. He's been on our radar and was a player we were really keen to bring in," he said. "Last season was a huge season for him following a couple of loan spells during which he developed.
"At Lens, he performed at such a consistently high level for a team that finished second in the league. Added to that was his form for Mali, where he became a really key player for them. He's a player that adds to a really good midfield that we already have; he also adds qualities that we don't have. He complements the current midfield."
Andrews added that Sangare's character stood out during discussions over the move: "From the conversations I've had with him, he's very keen to come here. He's a humble young man, but he's equally as determined to succeed in his career. He fits everything we want from a Brentford player, on and off the pitch. He'll be a player that I think will become very, very popular with the fans."
Sangare's path to west London was anything but direct. The Bamako-born midfielder started out at Yeelen Olympique before Red Bull Salzburg brought him to Austria in 2020, and rather than fast-tracking him into their first team, the Austrian giants spent the next few years farming him out — first to feeder club Liefering, then to Grazer AK, where he scored five goals in a productive 2021-22 campaign, before a switch to Belgium with Zulte Waregem and a return to Austria on loan at TSV Hartberg, where he clocked up 46 league appearances in a season and a half and established himself as a regular.
A permanent move to Rapid Wien followed in the summer of 2024, and it was from there that Lens paid around €13m to bring him to Ligue 1 the following August, kickstarting the breakout campaign that has now earned him a switch to the Premier League.
Internationally, he has 16 caps for Mali since making his debut in 2024 and played every match as his country reached the quarter-finals of the 2025 Africa Cup of Nations.