Benoit Badiashile, a defender for France, was acquired by Chelsea on Thursday from Monaco of Ligue 1 for a reported sum of little under 40 million euros ($42 million).
According to a release from Chelsea, the central defender, age 21, signed a "seven-and-a-half-year contract".
At Monaco, Badiashile has played a crucial role in helping the team consistently finish third in Ligue 1.
Didier Deschamps gave him his international debut in September of last year, but he was left off the World Cup roster.
“At 6ft 4in, Badiashile is a dominant defender in the air but equally comfortable with the ball at his feet, capable of playing short passes out from the back or switching the play with longer diagonals,” read the Chelsea statement.
“His blistering speed is a key attribute and he has experience in both a back four and back three at club level.”
Badiashile said he could not wait to “start playing in the best league in the world.”
The young Frenchman could partner the vastly more experienced Senegalese international Kalidou Koulibaly, who Chelsea signed for a reported fee of £33 million ($38 million) last July.
Chelsea chairman Todd Boehly and co-controlling owner Behdad Eghbali said they were delighted to have secured the signature of one of Europe’s most promising defenders.
“He’s an excellent young player who has quickly established a strong reputation for himself and has a huge amount of experience for his young age,” they said in a joint statement.
“We are sure he will form an important part of our team in the years ahead.”
Badiashile will not be involved in Chelsea’s clash at home to Manchester City on Thursday as they try and make up ground on the top four.
Chelsea is 10 points off the Champions League places following a New Year’s Day draw at Nottingham Forest and have won only one of their last seven matches.