Oct. 24 (UPI) -- The Premier League club announced the deal on Tuesday. Alonso is now tied to the club until 2023.
"I am so happy to stay here longer and to keep playing for one of the best teams in the world," Alonso said in a news release from Chelsea. "It's been a very good two seasons and I am looking forward to more."
Alonso, 27, began his senior career in 2008 with the Real Madrid B squad. He joined Bolton Wanderers in 2010. Alonso joined Fiorentina in 2013 and stayed there until 2016, going on loan to Sunderland in 2014.
He joined the Blues in August of 2016. Alonso also has three appearances for the Spanish national team.
"We are delighted to be extending Marcos' contract," Chelsea club director Marina Granovskaia said. "In the past two seasons he has developed into an important player for the club, demonstrating his outstanding ability and a fantastic attitude that has helped him become a Premier League champion and Spain international."
Chelsea battles FC BATE Borisov in the UEFA Europa League at 3 p.m. on Thursday at Stamford Bridge in London.