De Rossi (left) and DeGeneres have been together for about four years
US talk show host Ellen DeGeneres is to marry her partner, actress Portia de Rossi, after California lifted its ban on same-sex ceremonies.
"I am announcing I am getting married," DeGeneres told the audience during a recording of The Ellen DeGeneres Show.
"It is something of course that we have wanted to do and we wanted to be legal, and we are just very, very excited."
DeGeneres came out in 1997, and was in a relationship with actress Anne Heche until 2000.
She has been with Portia de Rossi, who appeared in the TV series Ally McBeal, for about four years.
Australian-born De Rossi, who was also in Nip/Tuck, was seen smiling and clapping in the audience when DeGeneres announced they were getting married.
DeGeneres joked: "Thank you. I'll tell you who the lucky guy is soon."
On Thursday, California's Supreme Court said the "right to form a family relationship" applied to all Californians regardless of sexuality.
But opponents of the decision said they would seek an amendment to the state constitution, which would override the ruling.