The 22-year-old defender, who represented Spain at this summer's Olympic Games, has moved to Stamford Bridge to bolster Roberto Di Matteo's defensive ranks
Roberto Di Matteo completes his fifth signing of the summer, having already concluded deals to bring Eden Hazard, Oscar, Marko Marin and Thorgan Hazard to Stamford Bridge, and the Spaniard looks set to solve the club's right back problem, after Jose Bosingwa left at the end of last season.
Marseille confirmed the deal on its official club website with a statement that read: "'Azpi' Chelsea, you're done." The transfer was formally concluded on Friday morning between OM and the British club, and the Spaniard has signed his contract.
"A new challenge awaits him in the ranks of the Champions of Europe 2012."
As revealed by Goal.com last week, the move has been on the cards for some time and with only Branislav Ivanovic in the current Chelsea squad capable of playing out on the right, ahead of a long and arduous campaign, the Italian boss has sought to add some much-needed depth to the squad.
Azpilicueta arrives after a successful two-year stay in Ligue 1 with Marseille, during which he established himself as a regular but following a disappointing 10th-placed finish last season.
The defender follows former boss Didier Deschamps out of the exit door at the Stade Velodrome this summer, after he left to replace Laurent Blanc as the coach of the France national team.
The 22-year-old boasts a wealth of experience, considering his age, having played for four years prior to his move to France in La Liga with Spanish outfit Osasuna, going on to make over 100 appearances for the club in the process.