The 40-year-old Australian, who left Fulham at the end of last season after five years at Craven Cottage, has signed a one-year contract at Stamford Bridge.
He told chelseafc.com: "It's a phenomenal club. It's one of the biggest and best clubs in the world, and it's an honour to sign for Chelsea. I didn't take much convincing to come here."
Schwarzer moved to England in 1996 to join Bradford before making 367 league appearances in 11 years with Middlesbrough. He won the League Cup with Boro in 2003 and appeared in the 2006 UEFA Cup final against Sevilla.
During his time at Fulham he became the first overseas player to make over 500 Premier League appearances and reached another European cup final as the Cottagers lost out to Atletico Madrid in 2010.
Schwarzer's contract with Jose Mourinho's Blues runs until the 2014 World Cup in Brazil, where the veteran keeper will hope to add to his 108 caps given Australia's qualification for the tournament.