Shepard quickly responded with a yes, the Los Angeles Times reported. The couple, who have been an item since 2007 and have a baby daughter, broke off their previous engagement, saying they would not marry until their gay and lesbian friends were free to do so.
Bell's proposal was simple: "@daxshepard1 will you marry me? Xo #marriageequality #loveislove."
The response was also short: "DOMA is dead. Prop 8 is dead. Now let's bring my big, gay marriage to @IMKristenBell to Life!!!!"
Shepard proposed the last time the couple got engaged, in 2010, the Times said.
Bell and Shepard co-starred in last year's "Hit and Run," which Shepard wrote and co-directed.