It's reported around 60,000 partnerships have been recorded since they were introduced in 2004.
Despite the Same Sex Marriage Bill allowing marriages to take place earlier this year, those in civil partnerships haven't been able to 'upgrade'.
As of today, couples will have the choice to convert in a local register office or to celebrate with a ceremony in approved premises or religious premises where marriages of same sex couples can take place.
The Equalities Office says couples will be issued with a marriage certificate which will show the marriage should be treated as existing from the date of the original civil partnership.
For the first year, all couples who formed their civil partnership before 29 March 2014, will be able to receive a £45 fee reduction. This means there will be no cost for the simple administrative process.
Jo Swinson, Minister for Equalities said: "Today we take the final step in implementing this historic legislation, by allowing couples to convert their civil partnership into marriage, if they want to.
"Congratulations in advance to all the couples already in civil partnerships who are planning to convert them into marriages in the coming months."
All the major church denominations have refused to opt into legislation which would allow their buildings to be used for gay weddings.
Quakers in Britain has opted in.
The Church of England led the opposition to the Same Sex Marriage bill when it went through Parliament last year.