The 23-year-old has put pen to paper on a seven-year deal at the Blues and will be the club’s No 1 following the departure of Thibaut Courtois.
The deal for Kepa outstrips the £66.8m paid by Liverpool for Alisson last month. The Brazilian was Chelsea’s first choice to replace Courtois.
Kepa couldn’t hide his excitement after completing his move. ‘It’s a very important decision for me, for my career, and also for my personal life.
‘So many things attracted me to the club, all the titles the club has won, the other players, the city, the English Premier League.
‘It’s an accumulation of things, and I am very glad Chelsea has decided to trust me and to take me in as well.’
Director Marina Granovskaia added: ‘Kepa is a talent we have admired for a long time and we are extremely excited about his arrival.
‘He has already demonstrated fantastic quality and consistency and will be a big part of any success Chelsea have in the coming years.
‘His long-term contract reflects the belief we have in him and we look ahead to the coming seasons with an enormous sense of optimism.’