Grainne Close of Northern Ireland and her American partner, Shannon Sickels, walked hand-in-hand from a black taxi for a 20-minute ceremony that featured an exchange of matching platinum and diamond rings and a recording of Dolly Parton's "Touch Your Woman."
"We just want to say that this is a very privileged position we are in this morning, and for us this is about making a choice," said Close, 32, who wore a black suit with a white scarf.
"This is about making a choice to have our civil rights acknowledged and respected and protected, and we could not be here without the hard work of many queer activists and many individuals from the queer community," said Sickels, a 27-year-old playwright from New York, who wore a white trouser suit.
Some of their approximately 70 guests, walking through city hall's wrought-iron gates, brushed off point-blank insults from Christian evangelists.
"You need to turn yourself away from your sinful lifestyle. You're an abomination before God," a Scottish preacher, the Rev. James Dawson, told one lesbian couple walking past.
"You would be so lucky to have this lady, love. I'll see you at the gates of heaven, mate," retorted Belfast woman Brenda Murphy, walking beside her partner, Nuala Quiery.
After the ceremony, Close and Sickels walked up to camera crews and proudly displayed the rings on their fingers before being driven away.
Three homosexual couples, one male and two female, were scheduled to sign the civil partnership register Monday in Belfast City Hall. The new law, which already exists in several other European countries, grants gay couples the same property and inheritance rights as married heterosexual couples.
The law went into effect in Northern Ireland one day before Scotland and two days before England and Wales, where more than 600 gay couples plan to gain legal recognition of their relationships Wednesday.
Northern Ireland in 1982 became the last part of the United Kingdom to legalize homosexuality. The province's considerable gay community frequently complains of intimidation and harassment in both Irish Catholic and British Protestant areas.
In its most recent report on the problem, the Police Service of Northern Ireland in May said the number of reported homophobic attacks in this territory of 1.7 million was escalating. It said crimes involving an anti-gay motive rose to 196, compared with 71 in 2003-04 and 35 in 2002-03.