The Kills rocker jetted out to Mustique last week (ends15Jan09) to celebrate his lover's birthday with a group of pals, including British retail tycoon Sir Philip Green.
And Hince, who has dated Moss since 2007, surprised the catwalk queen at her birthday bash by asking for her hand in marriage, according to Britain's Daily Mail newspaper.
A source tells the publication, "Kate was stunned, Jamie called her up and told her not to come home. He said he was flying out to Mustique.
"He had carefully picked a ring and chose her birthday to propose. It was the first time they had been alone together in quite a while and it was extremely emotional.
"Kate and Jamie are in a very good place, they already live together and this is the next step to settling down for good."
Moss - who has never been married before - has a daughter, Lila Grace, with ex-partner Jefferson Hack. She has also enjoyed lengthy romances with Johnny Depp and rocker Pete Doherty.