The 'Panic Room' actress - who confirmed she is gay at the Golden Globe Awards last year following years of speculation - tied the knot with the photographer in a secret ceremony over the weekend after almost a year of dating.
A spokesperson for the Oscar-winning star confirmed the happy news to E! News.
The couple started dating last summer and were first spotted attending a technology seminar at Fox Studios in Los Angles together.
A source previously said: "It's pretty serious. They are totally in love."
The 51-year-old star previously dated Cydney Bernard, with whom she has two sons, Charles, 15, and 13-year-old Kit.
She thanked her former partner, whom she split from in 2008 after 20 years together, while accepting a Cecil B. DeMille Lifetime Achievement Award at the Golden Globes in 2013, while addressing rumours about her sexuality for the first time.
She said: "This is not going to be a big coming-out speech tonight because I already did my coming out about a thousand years ago back in the stone age - in those very quaint days when a fragile girl would open up to trusted friends and family and co-workers and then gradually proudly to everyone who knew her."
Meanwhile, Alexandra previously dated Ellen DeGeneres for three years until 2004.