"It is of course a decision for the Northern Ireland Assembly, but I am confident that like other western European countries they will make that decision in due course," said Varadkar, Ireland's first openly gay leader who took office in June.
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Northern Ireland is the only part of Britain where same-sex marriage remains illegal, and the largest political party in the province, the Democratic Unionist Party (DUP), is deeply opposed.
The DUP, which has strong Protestant Christian fundamentalist roots, has consistently blocked the measure in the devolved assembly in Belfast.
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However, the party has been relatively restrained about Varadkar's participation in the Pride event, with DUP leader Arlene Foster saying it was "his own business".
The Republic of Ireland, a traditionally Catholic country, voted to allow same-sex marriage in a historic referendum in 2015.
Varadkar attended a Pride breakfast in Belfast although other commitments prevented him from staying for the parade through the city centre, which this year will include uniformed police officers for the first time.
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