The landmark Senate vote of 33-27 was carried live on Argentina national television.
The law tweaks the legal code which no longer will refer to husband and wife, but rather to “the marrying parties.”
The legislation, passed by the lower house in May, also gives same-sex couples the same rights as heterosexuals in terms of adoptions, social security and family time.
Argentina became the first country in Latin America to green light to same-sex marriage nationwide. It followed, around the world, the Netherlands, Belgium, Spain, Canada, South Africa, Norway, Sweden, Portugal and Iceland. Mexico City allows same-sex marriage.