The 62-year-old Stewart and his 36-year-old bride were hitched in a small town near the resort of Portofino with only two witnesses present and the town hall official presiding, People magazine reported.
The Stewarts have one daughter together, Alistar, who was born in late 2005. The Los Angeles-based singer was divorced in January from his second wife, Rachel Hunter, who also is a model.
People said Stewart had presented Lancaster with a sizable diamond ring.
Notable deaths of 2014 [PHOTOS]