Taoiseach Leo Varadkar says he believes it is only a matter of time before same-sex marriage is introduced in Northern Ireland.
Ireland's first openly gay leader was speaking as he attended a Pride breakfast event as Belfast gears up for its biggest march of the year.
Northern Ireland remains the only UK region where same-sex marriage remains outlawed.
The Republic voted to change the law in a watershed 2015 referendum.
Campaigners have mounted an increasingly vocal bid to overturn the restriction north of the border and 8,000 people are due to parade through Belfast city centre.
Mr Varadkar said his presence at a breakfast on Saturday morning as part of the Belfast Pride festival was not an attempt to unsettle anyone who holds a different view on same-sex marriage and conceded its introduction in Northern Ireland was the responsibility of local politicians.
It has been one of the sticking points preventing the return of a devolved power-sharing administration at Stormont, with Sinn Féin demanding the DUP stop blocking changes to the law.
The party has used the petition of concern mechanism to prevent the legalisation of same-sex marriage, despite a majority of Assembly members supporting the move at the last vote.
The DUP rejects any suggestion it is homophobic, insisting it is protecting the "traditional" definition of marriage, and has called for tolerance of what are increasingly minority views.
After March's Assembly election, the party no longer has enough members to veto a same-sex marriage vote on its own, but there is no immediate prospect of the deeply divided administration being restored.
A total of 8,000 people are expected to march from Custom House Square in the city centre and an estimated 15,000 additional supporters are anticipated, the Parades Commission, which rules on marches, said. Sixty bands are due to take part.
For the first time, representatives of the PSNI and the Garda south of the border will be marching in uniform.
A rainbow Pride flag has been raised at a UK Government building at Stormont for the first time.
The flag was raised beside Stormont House on Friday morning to mark the city's Pride festival.
LGBT+ Conservatives patron, Stuart Andrew MP, will take part in the Pride march along with thousands of local demonstrators.