Foreign Secretary Ed Miliband said both imports of goods and some services to and from Israeli settlements would come under the ban.
The UK - along with major allies such as France and Canada - has followed the path of some European neighbours as settler expansion and violence ramp up in the West Bank.
While trade in services between the UK and settlements is not outlawed entirely, advertising illegal settlements for sale will be prohibited.
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Also promised was "action" against specific companies and individuals which provide construction, infrastructure financing, or real estate services. However, Mr Miliband didn't name any specific person or entity.
"So to those who finance or facilitate illegal settlements, let me say this. You will face the full force of UK sanctions," he said in the Commons.
It follows the trade minister saying in July that the government had been working on a prohibition and was keen for it to also cover trade in services.
Chris Bryant said he was concerned about companies in the UK providing mortgages for settlement buildings, acting as estate agents for properties there, or giving accountancy or legal services to the areas.
The foreign secretary said the UK would also impose new sanctions on "extremist settlers" and refuse applications for arms sales and other exports that "materially contribute to the occupation" - though it's unclear what that phrase encompasses.
What's not included?
Notable for its absence was a blanket ban on trade in services as had been endorsed by Mr Bryant in July.
Similarly, there was no mention of a universal ban on exports to settlements, just on imports.
How will it work?
Rather than using the existing sanctions rules, Mr Miliband said the government would create a "new comprehensive sanctions regime" to give effect to the embargo.
He said the regime would be in place within six to nine months but didn't mention how the measures would be enforced.
The state currently enacts such measures via the Sanctions and Anti-Money Laundering Act (SAMLA).
Why is this happening?
Pressure has been mounting on the government to take action as Israeli settlements grow and Palestinians face increased violence and intimidation.
There have been escalating attacks on Palestinians in the West Bank and, in the past weeks, some have had homes besieged.
Israeli settlements in occupied Palestinian territory have rapidly expanded in recent years, with more planned by the Israeli government.
Latest plans by the Israelis to build about 1,200 homes, as part of the E1 programme of expansion in the West Bank, were described by Mr Miliband as an "unacceptable and destructive act".
Such outposts have long been opposed by the UK government, which believes them to be a breach of international law and a threat to a two-state solution between Israel and Palestine.
Also adding pressure is its July 2024 advisory opinion from the UN's top court, which said Israel's presence in the occupied territories was "unlawful".
The International Court of Justice (ICJ) said all UN member states were under an obligation "not to recognise as legal the situation arising from the unlawful presence of the state of Israel in the occupied Palestinian territory and not to render aid or assistance in maintaining the situation".
What are settlements?
A settlement is an Israeli-built village, town or city in occupied Palestinian territory - either in the West Bank or East Jerusalem.
Creating settlements can involve confiscating land and displacing Palestinians, which is illegal under the Geneva Convention, as is the moving of Israeli civilians into territory Israel occupies.
Mr Miliband told the Commons there was "ethnic cleansing of Palestinians in areas of the West Bank, perpetrated by settler terrorists" - with "houses bulldozed, roads and public infrastructure destroyed, families displaced from their homes".
Israel disputes this, saying it cannot be classed as an occupying power, as no country owned the land before it took the territory in 1967, and it has not transferred its population to the territories; people move freely.
Contrary to the UN, Israel officially recognises and administers some settlements.
Has this been done before?
Spain, Ireland, Belgium and the Netherlands have announced similar trade prohibitions previously.
But by implementing an embargo that spans both imports and exports of goods and some services, the UK has one of the most comprehensive bans in Europe.
Ireland and Belgium, for example, have only prevented trade in goods.
The foreign secretary said France and Canada would also ban trade from illegal settlements - and that Denmark, Finland, Iceland, Poland, Portugal and Sweden had pledged to "support further action".
What do opponents say?
Speaking ahead of the UK government announcement, Israeli president Isaac Herzog said it would be a "grave miscalculation, a decision that will fall on the wrong side of history".
He said sanctions would "directly harm" Palestinians, "robbing them of business and employment".
Shadow foreign secretary Tom Tugendhat told the Commons that illegal settlements were "wrong" and that "outrageous" crimes were being committed.
However, he said the sanctions would "harm innocents" because the Israeli and Palestinian economies are "too interconnected".
The US government hasn't yet officially responded. However, America's ambassador to Israel, Mike Huckabee, said before the announcement that sanctions were "irrational" and he did not "understand what it's supposed to achieve".
Other opponents are Labour Friends of Israel (LFI), which said the ban is "practically impossible and will become a de facto boycott of all of Israel, which would be deeply damaging to the UK national interest, the British Jewish community, and Palestinian workers".
Meanwhile, polling by YouGov suggested one in two Britons backed a ban.
