The 29-year-old has moved to Stamford Bridge after his contract at Fulham expired this summer.
Bettinelli spent last season on loan at Middlesbrough, where he made 42 appearances in all competitions.
Chelsea were on the lookout for a new third choice goalkeeper after Willy Caballero’s spell at the club came to an end this summer.
Bettinelli will provide support for Edouard Mendy and Kepa Arrizabalaga as he becomes manager Thomas Tuchel’s first signing since taking over from Frank Lampard in January.
On signing a two-year contract at Stamford Bridge, Bettinelli said: 'It’s always been a special club. I know the area very well so it’s been a dream of mine to come over to this side and it’s finally happened. There were some talks a few years ago when I was a bit younger and for whatever reason that didn’t come about but I’m here now.
‘I’m really excited to be involved and looking forward to trying to impress and help the team as much as I can.’
Chelsea will begin their 2021/2022 Premier League campaign with a home game against Crystal Palace on August 14.
The European Champions will however contest the UEFA Super Cup against Villarreal at Belfast’s Windsor Park on August 11.
