Northern Ireland is the only part of the British Isles where same-sex marriage remains outlawed.
The MSP and Christian, who recently became engaged to her partner Jen Wilson, will discuss the issue when she gives a lecture as part of Belfast's Pride celebrations.
"As a practising Christian, a protestant and a unionist who is engaged to a Catholic Irishwoman, for me, equal marriage isn't about one religion, country or community.
"It is about people in Northern Ireland being afforded the same rights as everybody else.
"Scotland is a better place today because of equal marriage and I want to take that positive message from our experiences here to Belfast and beyond."
Those opposed to gay marriage say it goes against what the Bible says about sexuality, and that same-sex couples already have equal rights via civil partnerships.
The DUP, the biggest party in the Northern Ireland Assembly, has consistently opposed a change in the law.
The Evangelical Alliance in Northern Ireland has criticised the comments.
Director Peter Lynas said: "Northern Ireland, like 170 countries around the world, recognises marriage as between a man and woman.
"We don't see marriage as an inequality to be righted but as a unique gift with the biological potential to create new life and social good for everyone.
"Sadly in a consumerist society some see marriage as just another product to be redefined to suit their own needs."