The Veronica Mars actress asked her partner to marry her on Wednesday to celebrate the United States Supreme Court's overturning of the Defence of Marriage Act (DOMA).
The 32-year-old's gay and lesbian friends are now able to tie the knot, leading them to arrange their own wedding.
"daxshepard1 will you marry me? Xo ," she posted on the micro-blogging website.
She popped the question after agreeing that the previous rules in place were unlawful.
Bell shared her views with over one million followers online.
"You're damn right DOMA is unconstitutional!! ," she wrote while also retweeting the similar views of others using the website.
Bell and Shepard had been discussing getting hitched for four years.
The father to her three-month-old daughter Lincoln responded enthusiastically to her proposal.
"DOMA is dead," he posted. "Prop 8 is dead. Now let's bring my big, gay marriage to IMKristenBell to Life!"
In August 2012, Bell told TV host Larry King that she and 38-year-old actor Shepard were waiting to marry because it was unfair on some of their friends.
She explained that until Proposition 8 was abolished she wouldn't take advantage of her own rights.
"The reason we're not rushing to get married is because I don't feel appropriate taking advantage of a right that's denied to my (gay and lesbian) friends," she said.
"I'll feel more comfortable having a party - or whatever we have, if anything - if half of our friends who are homosexuals (can celebrate). It's just kind of rude to invite everyone to a party for a rite not everyone can hold."
- Cover Media