As polls closed on Friday, activists expressed cautious optimism with surveys predicting that Ireland would recognize marriage equality, a position opposed by the Catholic Church, which lobbied hard against the measure. Officials will announce the results on Saturday.
If the referendum passes, Ireland would become 19th country in the world to recognize marriage equality and the 14th in Europe - as well as the first to do so by popular vote.
Referendums in Croatia and Slovenia both resulted in "No" votes, although Slovenia's parliament went ahead and recognized marriage equality in March. Northern Ireland continues to limit such unions to heterosexual couples, even though the rest of the United Kingdom recognizes marriage equality.
In the United States, the Supreme Court is examining marriage equality. In Austria, which does not allow homosexual marriages - though polls show the population overwhelming supports equality - Vienna has changed its crosswalk signals to feature same-sex couples as the capital hosts the Eurovision Song Contest finals this weekend.
The state broadcaster RTE reported that polling stations had recorded a higher turnout than usual for referendums, with voting levels in some areas predicted to top 60 percent, more comparable with that witnessed at general elections. Up to 3.2 million voters had been able to cast their ballots, with the result expected on Saturday afternoon.
'In the name of love'
All Ireland's main political parties, including conservatives, support amending the constitutional definition of marriage, and the final polls put their camp comfortably in the lead. However, that does not guarantee a positive result for supporters of marriage equality: The Catholic Church has campaigned strongly for a "No" vote, and many older and rural voters agree with the clergy. The majority of Irish people identify themselves as Catholic, although the church's influence has waned amid growing secularization and after a wave of child sex abuse scandals that badly discredited the hierarchy.
On Friday, Irish rockers U2 - whose singer, Bono, frequently draws on his Catholic and Protestant upbringing in the band's religion-tinged lyrics - tweeted a link to a picture of a handwritten note reading "In the name of love ... vote Yes." The tweet refers to "Pride" the second song off U2's fourth studio album, a paean to the American civil rights leader Martin Luther King Jr. easily adapted by the band to lend its support for a new rights movement.
As Ireland has no system for mailing votes in, citizens living abroad had traveled home to have their say. A second proposed amendment to lower the minimum age of presidential candidates from 35 to 21 did not seem likely to pass.
mkg/rc (Reuters, AFP, dpa, AP)