Britain's pledge to take on some of Syria's most vulnerable refugees will "transform the lives" of children, torture survivors and victims of sexual assaults, campaigners said.
No figure is being put on the number of displaced people the UK will take, but hundreds are expected to arrive over the coming year, after an announcement by Deputy Prime Minister Nick Clegg.
The UK is not signing up to take a quota of refugees under the United Nations sanctuary scheme to resettle up to 30,000 vulnerable Syrians in Western nations, but Clegg said the UN High Commission for Refugees backs the Government's plans.
Syrian children outside their tents at a refugee camp in the eastern Lebanese border town of Arsal
Home Secretary Theresa May will formally confirm the plans in a statement to the House of Commons on Wednesday, provoked by a debate called by Labour, which wants Britain to join the UNHCR scheme.
David Cameron has previously argued Britain taking refugees is not the solution to a crisis which has seen more than two million Syrians flee their homes during the bloody three-year civil war.
The UK has provided £600 million in aid to help victims of the violence in Syria and neighbouring countries.
After coming under pressure from Labour and Liberal Democrats, he told MPs at Prime Minister's Questions last week that he was ready to consider taking in refugees in cases of extreme hardship. May and Foreign Secretary William Hague have been working on details of the scheme over the past week.
Clegg said in a statement: "I am pleased to be able to announce today that the UK will be providing refuge to some of the most vulnerable Syrian refugees. The coalition Government wants to play our part in helping to alleviate the immense suffering in Syria.
"The £600 million we have provided makes us the second largest bilateral donor of humanitarian aid in the world. But as the conflict continues to force millions of Syrians from their homes, we need to make sure we are doing everything we can.
"We are one of the most open-hearted countries in the world and I believe we have a moral responsibility to help."
"The UN High Commission for Refugees - which backs our new resettlement programme - has said the highest priority should go to women and girls who have experienced or are at risk of sexual violence, the elderly, survivors of torture, and individuals with disabilities, so that's who we'll target.
"Sadly we cannot provide safety for everyone who needs it, but we can reach out to some of those who need it most.
"On top of that, we'll continue to support the peace talks currently taking place in Geneva, because only a political resolution between the (Bashar) Assad regime and Syrian opposition will provide a permanent end to the suffering.
"Britain has a long and proud tradition of providing refuge at times of crisis. This coalition Government will ensure it lives on."
No target will be set for the numbers of refugees to be admitted, with the UK instead working with the UNHCR on a case-by-case basis to identify those most in need of assistance.
Refuge will be offered to some of those most traumatised by the crisis, including vulnerable women and children, who are expected to arrive on a gradual basis over the coming months.
Shadow home secretary Yvette Cooper said: "Vulnerable Syrian refugees, torture victims, abandoned children and those struggling to cope or survive in the camps desperately need sanctuary and Britain has a moral obligation to help.
"I am very glad the Government has finally bowed to pressure before tomorrow's opposition vote.
The UK representative of the UN High Commissioner for Refugees, Roland Schilling, said: "This decision will help to provide much needed solutions for vulnerable Syrian refugees many of whom have been deeply traumatised and face immense hardship.
"It is also a concrete and important gesture of solidarity and burden sharing with the countries neighbouring Syria as they continue to bear the brunt of the refugee crisis.
"Today's decision is an encouraging and important step, reaffirming the UK's commitment and contribution to international relief efforts in support of more than 2.3 million Syrian refugees and the countries hosting them.."
Refugee Council chief executive Maurice Wren said: "This news, quite simply, will transform people's lives.
"What's more, it also sends an important message to the rest of the world: Britain has a proud tradition of protecting and welcoming refugees and we will continue to lead the way in offering refuge to people in their greatest hour of need.
"We commend the Government for upholding this reputation by going the extra mile and offering protection to some of the most vulnerable refugees who will now have chance to rebuild their lives in safety."
Amnesty International UK director Kate Allen said: "This move is long overdue but of course it's never too late to do the right thing.
"The government's line on this has been shameful, with months of refusal and weak arguments.
"It was a never a matter of choosing between helping refugees in the region or helping refugees in this country - and it's an enormous relief that the government has finally changed its mind on this.
"For some of the most vulnerable refugees, this offer is a lifeline. It's literally a matter of life and death."
"This is a welcome step to help some of the most vulnerable Syrian refugees even if it has been a long time coming and the numbers are relatively small," said an Oxfam spokesman. "Morally it is the right thing to do but it also sends an important message that other countries will support Syria's near neighbours in offering sanctuary to those forced to flee the violence.
"Ultimately it is peace and a return to a normal life that the people of Syria need and continued UK diplomacy will still be required to help bring an end to the bloodshed," said Oxfam.