The Catholic Church had opposed the legislation, which the Labour government promised to introduce as its first law after winning a second term last month and which the main opposition party supports.
The only question is whether the bill will pass unanimously on Wednesday or with a lone opposition lawmaker voting against.
The aim of the law, piloted by Equality Minister Helena Dalli, is to "modernise the institution of marriage" to give all consenting adult couples the right to marry.
Its passage is the latest evidence of the transformation of the once conservative island nation of about 440,000 people, where divorce was illegal until 2011.
While abortion remains banned in Malta, gay adoption has been legal since civil unions were introduced in 2014.
Last year, the number of exclusively civil marriages overshadowed the number of church weddings for the first time.
Archbishop Charles Scicluna has opposed the same-sex marriage law, reflecting the church's long-standing view that marriage is only between a man and woman.
Holy Matrimony will stay, so will the Christian's duty to respect each and every human being created in the image of God who is Love. pic.twitter.com/ykGDJDl8HN
— Bishop CJ Scicluna (@BishopScicluna) July 11, 2017
A few days after parliament started debating the legislation, he said: "I can decide that a carob and an orange should no longer be called by their name, but a carob remains a carob and an orange remains an orange.
"And marriage, whatever the law says, remains an eternal union exclusive to a man and a woman."
Prime Minister Joseph Muscat said it would be "discriminatory" to have separate laws for heterosexual and same-sex marriages. Therefore, amendments to existing laws include the elimination of any reference to "husband and wife". In its place is the gender-neutral term "spouse" to cover all situations.
The law also calls for the removal of the terms "father" and "mother", to be substituted by "parents".
Lesbian couples who have children via medical interventions are distinguished by the terms "the person who gave birth" and "the other parent".
Other changes concern heterosexual marriages: Any reference to "maiden name" is replaced with "surname at birth", while couples can now choose what name to take after marriage. The man, for example, can take his wife's surname.
More than a dozen European countries have legalised same-sex marriage, all in the western part of the continent.
According to the Pew Research Centre, almost a dozen others have some sort of same-sex unions or civil partnerships.
