There were 7,366 ceremonies in which those not already in a civil partnership tied the knot in the 15 months after the law was introduced in March last year.
Of those, 55% were between female couples and 45% male, the official data showed.
The average age at marriage for same-sex couples was 40 years for men, compared with 37 years for women.
The figures also showed that far fewer couples are entering into civil partnerships since the law was brought in, with the number nearly entirely collapsing.
The ONS noted: From February 2014, the number of civil partnerships formed each month began to fall notably when compared with the same month a year earlier.
“In December 2014, only 58 civil partnerships were formed compared with 314 in December 2013, a fall of 82%.”
In addition, there were 7,732 couples who chose to convert an existing civil partnership into a marriage between December, when they could first do so, and June this year.