Up to 10 million people on five continents are expected to turn out simultaneously in what organisers are billing as the largest peace rally ever.
From Antarctica to Australia marches have been confirmed in up to 400 cities spanning 60 countries to protest at the US-led plans to attack Iraq.
In Ireland, anti-war demonstrators will be bussed to the capital from all corners of the country to take part in what will be one of the largest marches Dublin has seen in recent times.
London and Barcelona are both preparing for up to half a million people, while other European capitals including Paris, Rome and Berlin are predicting crowds of up to 100,000.
In the US, a quarter of a million people are expected in New York while hundreds of thousands more are expected to take to the streets in another 140 cities and towns across America.
Dublin’s march, which is being organised by the Irish Anti War Movement (IAWM), kicks off at 2pm and is being supported by a wide coalition of groups, ranging from environmental movements to student bodies and most domestic trade unions.
Some Opposition TDs and MEPs have thrown their weight behind the event which will also be attended by numerous prominent artists and public figures.
Speakers include Labour’s Michael D Higgins and singers Mary Couglan and Hazel O’Connor. Gardaí have warned motorists to avoid the city centre during tomorrow’s march. Extensive traffic restrictions will be in place between 2pm and 5pm while sections of Parnell Square, St Stephen’s Green and Dame Street will at times be completely closed to all traffic.