The former AC Milan goalkeeper has signed a contract with the Stamford Bridge club until the end of the season.
The Blues moved for the 33-year-old after first-choice Thibaut Courtois was ruled out for three months with a knee injury.
Asmir Begovic has taken over the No.1 jersey in Courtois' absence with youngster Jamal Blackman being named on the bench.
But Amelia, who was linked with a move to Arsenal over the summer, will now provide experienced cover.
A club statement read: "Chelsea Football Club is delighted to announce the signing of Marco Amelia.
"The goalkeeper arrives on a free transfer to provide highly experienced cover following the injury to Thibaut Courtois last month, and has signed a contract until the end of the season.
"Amelia, a full Italy international, signed with Serie B side Perugia last season having previously spent four years with AC Milan.
"He began his career with Roma before making his name with Livorno, enjoying subsequent spells with Palermo and Genoa.
"The 33-year-old will wear the number 32 jersey, and will be available for our Premier League game against Aston Villa."
