The Little Britain star is believed to have proposed to his lover with a vintage engagement ring in Los Angeles.
Confirming the news, Walliams told The Sun: "It's true, we're engaged and blissfully happy. I wasn't planning to make a public announcement because I'm not a royal - yet."
Meanwhile, a source close to the comedian said: "David is head-over-heels in love with Lara and is over the moon that she said 'Yes'. She's his dream woman."
It is thought that Walliams, 38, phoned Stone's parents in Holland to obtain their blessing before asking for the 25-year-old's hand in marriage.
The couple started dating in May last year, but managed to keep their romance under wraps until November.