Speaking on the eve of nationwide vote, Kenny said Ireland could "create history" by becoming the first nation to cast a popular vote for gay marriage.
Kenny said voters' approval of a constitutional amendment to legalize gay marriage would represent an Irish civil rights breakthrough "that for generations gay people could never imagine."
"The 'yes' will obliterate, publicly, the remaining barriers of prejudice or the irrational fear of the 'them' and 'us' in this regard," said Kenny, a devout Catholic who nonetheless during his four years in power has pushed to reduce the church's influence on policy and state services.
All political parties and most lawmakers are on the "yes" side. That lopsided reality, common in Irish referendums, has rebounded in previous contests when some voters, confused by the issue at hand or alienated from the political establishment, voted "no" in protest.
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Catholic leaders and conservative pressure groups are arguing that legalization could produce surprising repercussions in Irish courts that could undermine traditional marriages.
"Marriage isn't just about two people falling in love. It's a much more complex and a much more important part of the way our society is built up," Martin said.
"My voting 'no' is not a vote against gay and lesbian people. It's against changing the definition of marriage," Martin said.