Iceland Prime Minister Johanna Sigurdardottir was among the first gay couples to marry Sunday as the country's new gay marriage law came into force, the Iceland broadcaster RUV reported.

The gay marriage bill, introduced on March 23, was approved by 49 out of 63 members of the Althingi parliament on June 12. The remainder abstained, making the vote unanimous.

The legislation is groundbreaking in that it does not alter marriage to a gender-neutral institution, but instead includes “man and man” and “woman and woman” among the definitions of marriage.

Marriage replaces Iceland's system of registered partnerships for gay and lesbian couples first enacted in 1996.

Sigurdardottir, 68, entered into a registered partnership with writer-playwright Jonina Leosdottir in 2002. The pair applied to have their partnership converted to a marriage on Sunday, the first day the legislation took effect.

The law grants gay and lesbian couples all the benefits and obligations of marriage, including adoption.

Opposition to the bill was muted in the only nation headed by an openly lesbian prime minister.

“The attitude in Iceland is fairly pragmatic,” Gunnar Helgi Kristinsson, a political scientist at the University of Iceland, told Reuters. “It [gay marriage] has not been a big issue in national politics – it's not been controversial.”

Sigurdardottir took over the reins of Iceland's government last year when voters overwhelmingly rejected the conservative Independent Party as the tiny island nation (pop. 320,000) faced a financial meltdown.

Sigurdardottir has two adult sons from a previous marriage.

Iceland joins six European countries – Belgium, the Netherlands, Spain, Norway, Sweden and most recently Portugal – in legalizing gay marriage.

Lawmakers in Argentina are also debating the issue.