The Gay and Lesbian Network has said it regrets that President Michael D Higgins was not able to sign the same-sex marriage legislation last night.
The measure gives effect to the result of May's historic same-sex marriage referendum.
The popular vote had to be embedded in law by both the Dáil and Seanad, a process which ended last week in the Upper House.
Yesterday, the Cathoireach of the Seanad, the Ceann Comhairle and the Chief Justice signed the Marriage Act 2015 into law, a move welcomed by long-time gay equality campaigners - with just a tinge of regret.
Kieran Rose of the Gay and Lesbian Equality Network said: "While we're delighted that the legislation has been signed into law, I suppose there's a bit of regret that President Michael D Higgins wasn't able to sign it because he had played such a significant role in advancing the rights of lesbians and gay men in Ireland."
The Constitution says every bill presented to the president for his signature must be signed by him on the fifth, sixth or seventh day after it is presented to him by the legislature.
As yesterday was the seventh day, and Mr Higgins was still on his visit to the United States, there was no option but to convene the Presidential Commission to sign the Bill.
