Cynthia Nixon (left) and Christine Marinoni
05/18/2009 AT 09:45 AM EDT
Cynthia Nixon announced her engagement to girlfriend Christine Marinoni at a Sunday rally in New York to support same-sex marriage, reports Access Hollywood
At the rally, which also attracted Gov. David A. Paterson and Mayor Michael Bloomberg, the Sex and the Coty
actress, 43, flashed the diamond engagement ring Marinoni, 42, gave her and said, "It's time already," reports New York's Daily News
Nixon and Marinoni began dating
in 2004, following the actress's 2003 split
from her companion of 16 years, photographer Danny Mozes, with whom she has two children: Samantha, 12, and Charles, 6. "When I first started dating my girlfriend and people got wind of it, I said, 'Yes, that's true,' " Nixon told PEOPLE
in May 2008.
About that same time, with California having legalized gay marriage (a law subsequently struck down
in the November 2008 election), Nixon told the News
, "In an ideal world, we'd like to in New York, when it becomes legalized."