A court in Cairo has banned "all activities" by the Muslim Brotherhood.
The ruling on Monday applies to the group, its NGO and "any organisation derived from it," judges said.
The court also ordered the interim government to seize the group's funds and establish a panel to administer its frozen assets until any appeal had been heard.
A Brotherhood source told Ahram Online the verdict would be appealed within ten days.
The Islamist group existed outside of Egyptian law for decades and was only officially registered as an NGO in March 2013.
The lawsuit was filed by the leftist Tagammu Party.
Monday’s verdict is not the only challenge to the 85-year-old Islamist group's existence.
On 2 September, Egypt's State Commissioners Authority, a body that advises the government on legal issues, recommended the Brotherhood's dissolution after claims circulated of its links to armed militias.
The authority’s recommendations - which are non-binding - were made in accordance with Law 84 of 2002, which prohibits non-government organisations and institutions from forming paramilitary groups.
Egyptian authorities launched a crackdown against the group following the ouster of president Mohamed Morsi — who hails from the group — by the military on 3 July following mass protests against him and the group.
The group's supreme guide, Mohamed Badie, and most of its high and mid-level leaders have been detained and face charges including incitement of violence against their opponents.
On 17 September, Egyptian prosecutors froze the assets of several senior Brotherhood leaders and other prominent Islamists as part of investigations into the incitement of violence at protests.
Mohamed Badie, deputy supreme guide Khairat El-Shater, secretary general Ezzat Ibrahim and senior member Mohamed El-Beltagy are among dozens of prominent Islamists targeted by authorities.