An extra 400,000 hectares of English countryside will be protected to support the recovery of nature under plans to be announced by Boris Johnson.
The prime minister will make the commitment at a virtual United Nations event later.
He is joining a global pledge from 65 leaders to reverse losses in the natural world by the same date.
National parks, areas of outstanding natural beauty and other protected areas make up 26% of land in England.
Mr Johnson will promise that the government will increase the amount of protected land in the UK from 26% at present to 30% by 2030.
The environment is a devolved matter but the government has said it will work with Scotland, Wales and Northern Ireland, as well as landowners, to increase the amount of protected land across the UK.
The prime minister will sign the Leaders' Pledge for Nature, which includes commitments to prioritise a green recovery following the coronavirus pandemic, deliver ambitious biodiversity targets and increase financing for nature.
Mr Johnson will say countries must turn "words into action" and "agree ambitious goals and binding targets".
"We cannot afford dither and delay because biodiversity loss is happening today and it is happening at a frightening rate," he will say.
"Left unchecked, the consequences will be catastrophic for us all.
"Extinction is forever - so our action must be immediate."
World leaders have often come together to strike deals over climate change, but a top level commitment on nature is much more rare.
Environmentalists are delighted - they say nature is in freefall and urgently needs protection as roads, railways, housing and farmland cover the Earth.
But they say Boris Johnson must lead by example. They point out that around half of existing Sites of Special Scientific Interest in the UK are in poor condition, many through lack of funding.
What's more, measures to protect wildlife in the Environment Bill are becalmed in the Commons for want of parliamentary time.
Campaigners say if the UK is really taking nature seriously it must avoid trade deals that damage wildlife.
It must also clamp down on imports of food that have caused environmental destruction overseas - such as beef farming in the Amazon.
Martin Harper, the RSPB's director of global conservation, said the 30% commitment could be a "huge step towards addressing the crisis our wildlife is facing".
"However, targets on paper won't be enough," he said. "Those set a decade ago failed because they weren't backed up by action."
Mr Harper said the pledge must be put into domestic law "as part of a suite of goals to restore the abundance and diversity of our wildlife, in every country in the UK".
Craig Bennett, chief executive of The Wildlife Trusts, said it was a "good start" but "a much greater level of urgent action" was needed to put nature into recovery, including rescuing wildlife sites currently in decline.
He said many National Parks and areas of outstanding natural beauty were "severely depleted of wildlife because of overgrazing, poor management or intensive agricultural practices", while around half of sites of special scientific interest were "in a poor state and suffering wildlife declines".