The pair met on the set of GoT, where Rose played Ygritte from seasons two to four and Kit still plays her character’s former lover Jon Snow.
But they kept their love quiet for a four years, officially stepping out together for the first time last year
The engagement was formally announced in The Times newspaper.
The couple's announcement stated: "Mr K.C. Harington and Miss R.E. Leslie.
"The engagement is announced between Kit, younger son of David and Deborah Harington of Worcesterhire, and Rose, middle daughter of Sebastian and Candy Leslie of Aberdeenshire.
Kit attended Worcester Sixth Form College when he was younger, where he studied Drama and Theatre.