International Development Secretary Douglas Alexander announced the money as part of an international response to the catastrophe.
Mr Alexander said:
"It is already clear that we are facing a major humanitarian crisis. Haiti needs help and it needs it now.
"The most pressing need is for international search and rescue teams - including firefighters from all over Britain - to get on with their work of saving lives.
"But at the same time there is an overwhelming requirement for food, water, sanitation, shelter and medicine among the people who have been made homeless.
"That is why the Department for International Development is providing money to help kickstart humanitarian relief in Haiti."
The UK contribution will be divided between a number of international agencies and appeals - dictated by an ongoing assessment of need on the ground.
Around $1.6 million will go immediately to the appeal launched by the International Federation of the Red Cross. Other likely priorities for the remainder of the funds include water, sanitation, health, food and shelters.
A further donation will be made once the United Nations announces its "flash appeal".