The court denounced the country for violating the rights of three same-sex couples after failing to recognize their unions.
Italy's Court of Cassation in February rejected gay marriage, saying that nothing existed within the Italian Constitution which stipulated extending marriage rights to same-sex couples.
But the court then said that gay people have the right to a “protective law” which ensures they have the same rights as unmarried Italian couples.
Although same-sex marriage and civil unions are illegal in Italy, some cities allow gay couples who wed abroad to be registered.
In May, 17 gay, lesbian and heterosexual couples signed the first civil unions registered in Rome.
The capital joined Naples, Milan and dozens of other towns and cities in ensuring formal recognition of the couples in their dealings with the municipal authorities and, in the case of certain companies, with their employers.
A bill that would allow for civil unions nationwide is currently being studied by a committee of the Italian Senate but faces considerable opposition from centre-right allies of Prime Minister Matteo Renzi.
The government has also faced mounting pressure to give same-sex couples more rights since Ireland voted to legalize gay marriage in late May, with Laura Boldrini, the president of Italy's parliament, arguing that it was time to legislate for civil unions.