The 'Little House on the Prairie' actress' boyfriend - whose best known for his role as Elliot Weston in 'thirtysomething' - popped the question over the Christmas break and the couple are over the moon to be getting married.
A source told People magazine: ''They are engaged and both are incredibly happy.''
Melissa returned to the spotlight last year as a celebrity contestant on show 'Dancing With the Stars', in which she came in fifth place with her professional partner Maksim Chmerkovskiy.
This will be the third marriage for both the 48-year-old star - who has children Michael, 17, and 23-year-old Dakota with ex-husbands Bo Brinkman and Bruce Boxleitner - and Timothy, who has kids Daisy, Wilson and Samuel.
Timothy has appeared on the small-screen more recently in 'The Mob Doctor', 'Childrens Hospital' and 'Blue Bloods'.
He also directs TV shows such as 'Damages', 'Without a Trace' and 'Lipstick Jungle'.