The Hollywood couple married at an intimate ceremony inside the grounds of their $US29 ($NZ41) million Beverly Hills estate.
DeGeneres, one of America's top TV talkshow hosts, and Geelong-born actress de Rossi, both wore designs by Zac Posen as they exchanged written wedding vows.
The ceremony was attended by 19 guests, including DeGeneres' mom, Betty, and de Rossi's mother, Margaret Rogers, who had flown in from Australia, People.com reported Saturday night.
DeGeneres said after winning her fourth consecutive Daytime Emmy for talk show host in June that a date had not been set, and that she would show "a tiny bit" of the nuptials on her show.
DeGeneres, 50, and de Rossi, 35, began dating in late 2004.
The couple has joined thousands of others in California taking advantage of the state's landmark court ruling in May allowing gay marriage.
De Rossi was born Amanda Lee Rogers and was raised in Geelong, but chose the slightly grander name Portia de Rossi when she was 15.
The actress starred in the 1994 Australian movie Sirens with Elle Macpherson and moved to the US where she had a role in 1997's teen horror film Scream 2. Her big break was a leading role in the 1997 legal comedy TV series, Ally McBeal.
While opponents in California have gathered signatures to put a measure on the November ballot for a constitutional amendment to ban gay marriage, Hollywood was throwing its support behind the newlyweds.
"One of my favorite people of all time is Ms. Ellen DeGeneres," Katherine Heigl, star of "Grey's Anatomy," told Associated Press Television News at a Hollywood charity event on Saturday night.
"So I wish all the best, all the happiness, all the joy that comes with that certificate ... just the joy of being able to stand up and say that. In front of everyone you love and care about in front of each other and to walk away legal is huge."
AAP and AP.
