Same-sex marriage legislation is expected to be supported in a final vote at the Scottish Parliament today.
A free vote will determine the controversial issue which has polarised opinion among those who see it as a victory for equality and those who see it as an assault on religious tradition.
All couples in Scotland should be given the same rights, regardless of gender, according to the Scottish Government's Health Secretary, Alex Neil.
"We have always maintained at the heart of this issue there is one simple fact: a marriage is about love," he said.
"All couples in Scotland in a loving relationship must know that they have the same rights and responsibilities, and regardless of their gender, the same opportunity to get married."
Legislation to allow gay marriage in England and Wales was passed at Westminster in July last year.
The Marriage and Civil Partnership (Scotland) Bill, while sending a "clear signal" about equality, also takes account of celebrants who do not want to take part in ceremonies, Mr Neil said.
"I hope that our national parliament takes this opportunity to send a clear signal that our Scotland is a modern and progressive beacon for all, standing as passionate promoters and defenders of equality," he said.
The Bill puts belief celebrants, such as humanists, on the same footing as religious celebrants and allows civil partnerships to change to marriage.
The final debate will be a last chance for opponents to alter the legislation.
SNP backbencher John Mason is attempting to add a "protection" for people who believe marriage is between a man and a woman.
His party colleague Richard Lyle wants assurances that opponents of gay marriage will not have their views used against them when trying to adopt or foster children.
Labour MSP Siobhan McMahon is also trying to add protections for "freedom of expression".
The Equality Network charity will rally at Holyrood where they hope to see the Bill passed in a "defining moment" for gay people.
The Humanist Society of Scotland is marking the occasion by offering to conduct free conversion ceremonies for the first 100 same-sex couples who want to be married but are currently in civil partnerships.
Humanist celebrant Ross Wright said: "I've had the privilege of conducting wedding ceremonies for both heterosexual and homosexual couples, and for me, the only difference has been the gender of the dolls on the cake."
More than 50 ministers and church officials wrote to the Government at the weekend to express their ''deep concern'' over the proposed law.
Scotland for Marriage, a group set up to oppose the Bill, said more than 54,000 people had signed its petition by Monday evening.