CAIRO — Egypt’s highest court today ordered the country’s Islamist-dominated parliament dissolved, saying its election about six months ago was unconstitutional.

The Supreme Constitutional Court ruled today that a third of the legislature was elected illegally. As a result, it says in its explanation of the ruling, “the makeup of the entire chamber is illegal and, consequently, it does not legally stand.”

The ruling means that new elections for the entire parliament will have to be held.

The law governing the parliamentary elections, held over a three-month period starting in November, was ruled unconstitutional by a lower court because it breached the principle of equality when it allowed party members to contest a third of seats set aside for independents. The remaining two thirds were contested by party slates.

In a separate ruling, the court said Hosni Mubarak’s last prime minister, Ahmed Shafiq, could stay in the presidential race, rejecting a law passed by parliament last month that barred prominent figures from the old regime from running for office.

Shafiq will go head-to-head on Saturday and Sunday in a runoff against Mohammed Morsi of the Muslim Brotherhood, the country’s strongest political group.