Representatives for both actors have confirmed the engagement to People magazine.
Paquin plays Sookie Stakhouse in the HBO vampire show and Moyer plays her vampire lover, Bill. Paquin, 27, and Moyer, 39, began dating in February.
Paquin told AOL Television that their relationship made filming steamy sex scenes easier.
"Obviously, if you're already with that person then you're not having to sort of get over the 'Wow, I'm naked with someone that I don't even know the middle name of!'" she said.
Paquin was 11-years-old when she won a Best Supporting Actress Oscar for her role in Jane Campion's film The Piano.
Earlier this year she won a Golden Globe for Best Performance by an Actress In A Television Series - Drama for her performance in 'True Blood'.
