The event on Tuesday, organised by the Stop the War Coalition and Campaign for Nuclear Disarmament (CND), will mark the second anniversary of a huge anti-war march, which attracted more than one million people to the British capital in an ultimately futile bid to stop the March 2003 invasion to topple Saddam Hussein.
"This day of action will remind us of the horror people were trying to prevent and the continued opposition to the occupation," said Kate Hudson, the chairwoman of CND.
"Over the last two years the illegal invasion and occupation of Iraq has created massive suffering. No weapons of mass destruction have been found, and the hunt for them has been called off by the US," she said.
"Reports indicate over 100,000 Iraqi fatalities and more than 1400 US-led coalition troops have been killed."
As part of the rally, anti-war protesters are expected to sit down on the road, simulating death, disrupting traffic in the centre of London.
Galloway is demanding British
soldiers be brought home
"Students have called this die-in to highlight these ongoing deaths and to demand our government sets an early date for troops to withdraw from Iraq," said Peter Leary, of Student CND.
Other events will be held in towns and cities nationwide, including a peace vigil in Canterbury, another die-in in Plymouth and leafleting outside an army recruitment office in Edinburgh.
In addition, the organisers plan to hold another demonstration in London on 19 March - two years after the war began - to demand that British troops be brought home.
Peace campaigners uttered a similar cry at a rally in London on Monday night.
"We want to bring our soldiers home," said George Galloway, a Member of Parliament for the anti-war party Respect.
"We know that the overwhelming majority of the poor, bloody infantry in the British armed forces have been conscripted by unemployment, low pay and poor opportunities and sent to do the imperialists' dirty work in Iraq."
Adding to the sense of outrage, a Territorial Army soldier is due to resign on Tuesday because of his opposition to the Iraq war.
Lance Corporal George Solomou, 38, who believes the Middle East conflict is illegal and corrupt, plans to hand in a letter of resignation to his commanding officer in London, Britain's domestic Press Association reported.
The Territorial Army is a part-time reserve force that makes up about a quarter of British Army personnel.
On the day of the rally the US military announced that one more US soldier had died in Iraq. He was wounded by a bomb planted near Baquba, 65km (40 miles) north of Baghdad and died on Monday.
He was with soldiers on patrol when the bomb exploded. His death takes the US military death toll in Iraq to 1113 since the US-led invasion in March 2003.