The 34-year-old is engaged to camera assistant Preston J. Cook, her rep confirms to PEOPLE.
The pair got engaged on Christmas Eve at a private residence in Isla Grande, Colombia.
Cook, who worked most recently on Leonardo DiCaprio's The Revenant, and Stiles met on the set of 2015's Go With Me. Stiles, who is set to next appear in the latest installment of the Bourne franchise, shared a photo of her beautiful ring on Instagram, Monday.
"Best Christmas Ever!" she wrote.
Stiles and Cook have yet to set a date for their nuptials, according to her rep.