The 46 year-old actor posted a video showing him and Scott, 50, in a car wearing casual clothes on their way to get married in California.
In the video - posted on on photo and video-sharing site WhoSay - John says: ‘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?’
The star then turns the camera to Scott, who replies: ‘To get married. Yay!’
John thanks Supreme Court for making marriage legal in the state, saying: ‘We're getting married in the state of California. Thank you Supreme Court, about time you made it legal. See you after we have the ceremony!’
The newly-married couple later posted a picture of themselves holding their marriage certificate, writing: ‘We are now legally married. Thanks for all your great wishes. JB and Scott.’
John first announced the wedding plans on Twitter late last night, writing: ‘We are getting married today because we now can. Thank you Supreme Court.’
John and Scott previously entered into a civil partnership in the UK in 2006, but always vowed to marry formally as soon as it became legal to do so in America. Their wedding comes days after Gay Pride parades were held in San Francisco, California and across the world to promote equal rights.
The Torchwood star has previously revealed that he and Scott would like to adopt an older child in the future, telling a UK newspaper last year: 'We haven't ruled out having children ourselves but it depends where my career takes us.'
'We wouldn't want a baby. We'd look at adopting an older child or teenager who might have been in trouble. We would also look at adopting a gay child, thrown out of their home because of their sexuality.'