This means that the biggest obstacle to holding elections has been removed.
The top court was ruling on whether various aspects of the electoral law, known as Italicum, complied with the Italian Constitution. Most aspects were passed, though others, which did not fit in the perfect bicameral system preserved in December's referendum, were declared illegititimate in Wednesday's ruling.
The law had first been drawn up to apply only to the Lower House, because the Italian Senate was set to be reformed under a set of constitutional reforms proposed last year.
Hearings on Italicum's constitutionality were postponed to avoid interference with the referendum, which saw the proposed reforms overwhelmingly rejected in December.
This meant that when prime minister Matteo Renzi resigned, having staked his leadership on the reforms package, the country was left with neither a prime minister nor a workable electoral law.
President Sergio Mattarella held off on calling for elections until after the Constitutional Court had ruled on Italicum, despite calls from the numerous opposition parties to hold early elections.
In the ruling, which was finally announced shortly after 5pm, having first been scheduled for 1-1:30, most aspects of the law were ruled legitimate. Some aspects however were rejected, including a run-off, which wouldn't have worked in the perfect bicameral system.
On the morning of Wednesday's ruling, ex-PM Renzi posted a blog post on the theme of "starting again", a possible suggestion that the 42-year-old plans to run in the next election.