The actors planned on just obtaining a marriage license at the Beverly Hills County Clerk Office, but when an employee offered to marry them on the spot, they agreed. The private ceremony was held in a nearby courtroom.
A photographer was on hand to record the special moment, and Bell got emotional during the ceremony, according to the website.
The couple previously made a pact not to tie the knot until same-sex marriage was legal in the United States. Gay unions are now recognized by many states, including California.
Earlier this month, Bell told E! News: "I have to unfortunately report that we just haven't got it together on a Saturday to get to the court house. But we have every intention to.
"We want to sign those papers. And I think we just found out that you can do it online now. What if we got married online? Print it out, 'You guys, married! Married, everybody!' It's just out of laziness that we haven't actually done it yet."
She explained earlier this summer: "We're not having a wedding. It's not a desire of either of ours to have any sort of day of celebration for us. I feel like we get enough attention in our daily lives and we just want something sort of private that involves pen and paper."
The couple welcomed their daughter Lincoln in March.