It says the money will provide aid for more than 57 million of the most vulnerable people around the world.
The UN humanitarian chief said the level of need was "unprecedented".
The request comes as aid agencies warn they are running out of cash to fund this year's operations in Syria.
Last week the World Food Programme announced it would have to cut food rations to Syrian refugees.
'Rising scale'
The UN is requesting $2.8bn to help those displaced by the conflict inside Syria.
It is seeking another $4.4bn to help more than 3,250,000 Syrian refugees registered in neighbouring countries.
"The rising scale of need is outpacing our capacity to respond," said UN Undersecretary-General for Humanitarian Affairs Valerie Amos. "The crises in Central African Republic, Iraq, South Sudan and Syria will remain top humanitarian priorities next year."
Ms Amos said those conflicts accounted for more than 70% of the funding being sought.Other major crises covered by the appeal include Afghanistan, DR Congo, Myanmar, Palestinian territories, Somalia, Sudan, Ukraine and Yemen.
However, the UN said it did not include nine countries in Africa's Sahel region, which will be addressed in a separate request in February.
UN High Commissioner for Refugees Antonio Guterres said: "This is not business as usual in the humanitarian world. Today's needs are at unprecedented levels, and without more support there simply is no way to respond to the humanitarian situations we're seeing."
The BBC's Imogen Foulkes in Geneva says relief never happens overnight - aid agencies need to plan, but to do that they need cash.
Food and medical supplies for refugees have to be purchased in advance, and field hospitals have to be delivered and built.
