The couple dated for more than 20 years before tying the knot less than one week after the U.S. Supreme Court upheld a lower court ruling declaring California's Proposition 8, which barred same-sex marriages, unconstitutional.
"It's five after one and we've got our coffee and we're in the car getting ready to leave because where are we going, Scott?" Barrowman said in a video clip he posted online Tuesday.
"To get married. Yay!" Gill said.
"We're getting married in the state of California," Barrowman said. "Thank you, Supreme Court, about time you made it legal. See you after we have the ceremony!"
The newlyweds later posted a photo of themselves holding their new marriage certificate and showing off their wedding bands.
"We are now legally married," they said in an accompanying message. "Thanks for all your great wishes. JB and Scott."
Barrowman is known for his roles in "Torchwood," "Doctor Who" and "Arrow."