In the same year, she won a Teen Choice Award for the same role as Willow.
The star was married to Buffy co-star Alexis Denisof, who played Wesley, in 2003 and they have two daughters.
They live in California, and in 2002 Hannigan bought a home in Santa Monica, which she later listed for $5.1million (£3.7million).
Fans have been rewatching the star in Buffy, since the series was picked up by Amazon Prime Video and, later, All 4.
In the series she played the kind and quirky friend of Buffy Summers, who had special abilities as a witch.