The actors have been together since 2007 and have a 7-month-old daughter, Lincoln, born in March. They have always maintained they would not wed until gay couples could legally do so in the state of California.
"We would feel weird taking advantage of a right that's not available to certain citizens of the state we live in," Bell, who stars on House of Lies, told PEOPLE in August 2012.
Added Parenthood's Shepard: "When they legalize marriage for everyone ... we will get married."
Shepard popped the question three years ago, giving Bell what she called a "real cool piece of jewelry." (Indeed: her Neil Lane ring features a fancy-colored, 3 carat emerald cut diamond.)
But the low-key couple had no plans for a big ceremony. "We will not have a wedding, we will just quietly get married," Shepard said at the time.
The couple made good on that plan, making it official with minimal fanfare in Los Angeles on Thursday.
That's just the way both wanted it. "I don't fault anyone who wants a big day – especially girls," Bell told PEOPLE. "[But] we get more than enough attention in our everyday lives. I also wear more than enough party dresses."