The 1954 Hague Convention was set up after World War Two but has never been adopted into law by the government.
Culture Secretary John Whittingdale says destruction and looting in Syria and Iraq by Islamic State militants shows it is now essential.
The UK is the only major nation not to have endorsed the convention.
More than 115 countries are party to the agreement, including all United Nations Security Council members, except for the UK.
The Hague Convention was meant to ensure nations and armies would not target cultural treasures.  The UK was one of the original signatories to the convention but it was never ratified.
The 1990s conflict in the Balkans saw the agreement revised and in 2004 the UK said it would ratify when time allowed.
Mr Whittingdale says the convention will now become law in the UK "at the first opportunity".
He said: 'While the UK's priority will continue to be the human cost of these conflicts, I am in no doubt we must also do what we can to prevent any further cultural destruction.
"The loss of a country's heritage threatens its very identity."
A fund to support future intervention by archaeologists to recover at-risk monuments in Iraq, Syria and Libya is also reportedly to be set up by the government at a summit in September.
Professor Peter Stone, a leading campaigner for the convention's adoption, says it was "fantastic news... as long as there are no further delays".
Shadow culture secretary, Chris Bryant, who says Labour is committed to prompt ratification, said earlier this month that he was "at a loss to understand" why the government had not yet acted.
The director of the British Museum, Neil MacGregor, is also among those to have called on the UK to ratify the convention.
IS militants have been accused selling Syria's cultural heritage to raise funds, leading to a UN ban in the trade of artefacts from the country.
There are fears the militants may destroy the 2,000-year-old Roman-era ruins in Palmyra in Syria, while in Iraq the ancient Assyrian city of Nimrud is among the sites they have targeted.

The girl said during a TV interview the child would be "like having a doll".
Experts criticised Mr Pinera's comments as having no scientific foundation.
Mr Pinera supports Chile's abortion laws, which outlaw the practice in all circumstances. His critics want it legalised in cases of rape, and want the girl to be allowed an abortion.
The 11-year-old girl appeared in a TV interview on Monday, saying: "I'm going to love the baby very much, even though it comes from that man who hurt me.
"It will be like having a doll in my arms."
The girl was raped repeatedly over a two-year period by her mother's boyfriend, who has since been arrested.
Mr Pinera said he had asked the health minister to personally look after the girl's health.
"She surprised us all with words showing depth and maturity when she said that, despite the pain caused by the man who raped her, she wanted to have and take care of her baby," he said.
Forensic psychologist Giorgio Agostini said the girl would not have the mental or emotional capacity to understand her situation.
Sources: World Health Organization, Guttmacher Institute
"What the president is saying doesn't get close to the psychological truth of an 11-year-old-girl," he told the Associated Press news agency.
"It's a subjective view that is not based on any scientific reasoning."
The girl's case has already sparked a public debate about abortion.
Campaigners argue that the laws, which date back to the authoritarian rule of Gen Augusto Pinochet, should be changed to allow for abortions in cases of rape or when the mother's health is at risk.
Michelle Bachelet, the likely presidential candidate next year for the left-leaning opposition, supports the campaign.
Ms Bachelet earlier commented that the 11-year-old girl need to be protected.
"I think a therapeutic abortion, in this case because of rape, would be in order," she said.
Chile is one of seven Latin American countries where abortion is completely banned.
Last month, the case of a seriously ill woman in El Salvador made international headlines when the courts upheld the ban on abortion even though the woman's life was at risk and the foetus was unlikely to survive.
She was eventually allowed to have a caesarean section.
A major international agreement designed to protect cultural property during military conflict is to be finally ratified by the UK.
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Chilean President Sebastian Pinera has praised as "brave and mature" a pregnant 11-year-old rape victim who said she was happy to have the child.