Demonstrators marched to Downing Street to demand action for Darfur.
The UN assembly in New York next week is due to urge international governments to step up to their responsibilities in the war torn region.
Campaigners are demanding the full and swift deployment of a recently authorised peacekeeping force and calling for international pressure on all sides until attacks on civilians stop.
The march coincides with the second anniversary of the UN "responsibility to protect" agreement. This saw world governments vow to act to stop genocide and mass atrocities wherever they occur in the world.
But two years after that declaration campaigners say the international community has yet to fulfil their commitments to Darfur, where more than 200,000 people have been killed.
The march saw demonstrators march from the Sudanese Embassy through the capital to Number 10.
Bearing placards that said : "Darfur: Don't Look Away" and "Protect Darfur", they chanted: "Stop killing in Darfur" and "Peace for Darfur".
David Brown of genocide prevention organisation the Aegis said: "This is the second anniversary of the commitment by world leaders at the UN world summit of the responsibility to protect people at risk of genocide.
"The UN have the authority for a force of 26,000 peacekeepers to go into the region. There is very widespread concern that the timetable for deploying this is going to slip."
Mr Brown said for the peacekeeping force to work effectively it needs to have a very clear steer from political leadership. "Otherwise it's going to end up making a bad situation worse," he said.
