Jolie also will be the voice behind the company's new charity created in support of children's issues and causes, it was announced Thursday.
"Angelina Jolie embodies so many qualities of what St. John represents. She is strong, independent and dynamic. She's a mother, actress and a philanthropist," Richard Cohen, chief executive officer of St. John, said in a statement.
St. John's new advertising campaign with the 30-year-old actress, set to launch in spring 2006 publications, will be shot by photographer Mario Testino.
The ad campaign's creative direction will "take inspiration from the company's native California and will evoke a mood synonymous with effortless, Hollywood glamour," the company said.
In a statement, Jolie said: "I am a working mother who has set goals to accomplish a lot in this world. I want my wardrobe to be beautiful, sexy and comfortable — all at the same time. St. John is all of those things."
Supermodel Gisele Bundchen starred in St. John's fall advertising campaign.