Right wing Labor MP Tony Burke has declared his support for same-sex marriage, arguing the best thing for community cohesion would be for the change to be legislated as soon as possible.
In a statement published on his website on Sunday, Mr Burke said Ireland's decision to vote for same-sex marriage over the weekend should leave no politician in any doubt that the legalisation of same-sex marriage in Australia was inevitable.
Mr Burke, said his western Sydney electorate of Watson was out of step with national opinion in that it did not support change, and he had reflected this sentiment by voting against same-sex marriage in 2012.
But Labor's finance spokesman said the debate on same-sex marriage was becoming "harsher and angrier" and would only become more divisive.
"We need to get to the next stage of the conversation to explain why those who do not want the change will be unaffected by it."
Same-sex marriage advocates welcomed Mr Burke's change of heart, which they estimated would bring them within three votes of majority support for the change in the house of representatives if Liberal MPs were granted a free vote. Campaigners believe there is a slim majority in support of same-sex marriage in the Senate.
Prime Minister Tony Abbott on Sunday ruled out Australia following Ireland's example and settling the issue by a popular vote, saying it was a matter for parliament to decide.
Mr Abbott acknowledged the issue was important to millions of Australians, but said his immediate priority was boosting small business confidence through measures announced in the budget.
"This is obviously a serious issue, a very serious issue," Mr Abbott said.
"There are a range of views inside the Parliament; there are a range of views inside my party room; frankly there's a range of views inside my family.
"Inside the Abbott family I'm probably the last holdout for the traditional position," he added.
Mr Abbott's sister Christine Forster is a lesbian who has been with her partner Virginia Edwards since 2003.
The Liberal Party's current position it to oppose change to marriage laws, however Mr Abbott has left open the possibility of Liberal MPs getting a free vote on the issue in the future.
"If it comes before our Parliament again, our party room will deal with it. Our party room will decide whether our existing policy continues or not, and then we'll have a good debate," Mr Abbott said.
Liberal Democratic Party Senator David Leyonhjelm introduced a bill for same sex marriage in the Upper House last September, but the Liberal party room has not formally considered it.
The Labor Party's platform supports same-sex marriage, but MPs have a free vote on the issue.
Opposition leader Bill Shorten, who personally supports same-sex marriage, described the Irish result as "very exciting".
The result was also applauded by Irish Qantas chief executive Alan Joyce, who is openly gay.
"I'm incredibly proud that Ireland has become the first country in the world to legalise same-sex marriage by popular vote," Mr Joyce wrote on LinkedIn.
"Until 1993, homosexuality was a crime in Ireland; today Ireland is a world leader on social justice.
Mr Joyce has been with his partner Shane Lloyd for 15 years and has lamented not being able to marry him in the country where they both have passports, Australia.
