The ratification of this law was not devoid of conflict, despite support from 66% of the population. Roman Catholic authorities in particular were adamantly opposed, criticising what they regarded as the weakening of the meaning of marriage. Other associations expressed concern over the possibility of lesbians and gays adopting children. Demonstrations for and against the law drew thousands of people from all parts of Spain. After its approval, the conservative People's Party challenged the law in the Constitutional Court.

Approximately 4,500 same-sex couples married in Spain during the first year of the law. Shortly after the law was passed, questions arose about the legal status of marriage to non-Spaniards whose country did not permit same-sex marriage. A ruling from the Justice Ministry stated that the country's same-sex marriage law allows a Spanish citizen to marry a non-Spaniard regardless of whether that person's homeland recognizes the partnership. At least one partner must be a Spanish citizen in order to marry, although two non-Spaniards may marry if they both have legal residence in Spain.

The November 2011 general election delivered a landslide victory to the People's Party, whose leader Mariano Rajoy said that he opposed same-sex marriage, but any decision about repealing the law could be made only after the ruling of the Constitutional Court. On 6 November 2012, the law was upheld by the Court with 8 support votes and 3 against. Minister of Justice Alberto Ruiz-Gallardón announced that the government will abide the ruling and the law will not be repealed.