The French international central defender, who generally operates on the right side of a pair, will join for a figure believed to be around £38 million, claims David Ornstein of The Athletic.
The 25-year-old defender joined Monaco from Reims in 2020, emerging as one of their most consistent performers, and has been regularly linked with a move to the Premier League over the course of the last year.
He had been rumoured to interest Manchester United amongst others but now appears on course to start his career in England at Stamford Bridge, becoming one of the first signings for new Chelsea boss Mauricio Pochettino.
He joins Christopher Nkunku, Nicolas Jackson and Angelo Gabriel as a summer signing for Chelsea, and he will be reunited with his former colleague from his days at Monaco, Benoit Badiashile, who joined the club in January.
Chelsea have been in the market for a central defender since an injury to Wesley Fofana which could keep him out for much of the season, and the rumoured continued interest from Brighton in Levi Colwill, who was on loan on the south coast in the previous campaign