Climate advocates reacted with surprise and delight to Joe Manchin’s decision to back a sweeping bill to combat the climate crisis, with analysts predicting the legislation will bring the US close to its target of slashing planet-heating emissions.

The West Virginia senator, who has made millions from his ownership of a coal-trading company, had seemingly thwarted Joe Biden’s hopes of passing meaningful climate legislation – only to reveal on Wednesday his support for a $369bn package to support renewable energy and electric vehicle rollout.

The move by the centrist Democrat shocked many of Manchin’s colleagues, who despaired after more than 18 months of seemingly fruitless negotiations with the lawmaker, a crucial vote in an evenly divided Senate.

“Holy shit,” tweeted Tina Smith, a Democrat from Minnesota. “Stunned, but in a good way.”

Should the bill pass both chambers of Congress and be signed by Biden, it will be the biggest and arguably first piece of climate legislation ever enacted by the US. The world’s largest historical carbon polluter has repeatedly failed to act on the climate crisis due to missed opportunities, staunch Republican opposition and the machinations of the fossil fuel lobby.

The climate spending, part of a broader bill called the Inflation Reduction Act, “has the potential to be a historic turning point” said Al Gore, the former vice-president.

“It represents the single largest investment in climate solutions and environmental justice in US history. Decades of tireless work by climate advocates across the country led to this moment.”

The bulk of the bill includes hefty tax credits to unleash clean energy projects such as wind and solar as well as a rebate of up to $7,500 for Americans who want to buy new electric vehicles. There is $9bn to retrofit houses to make them more energy efficient, tax credits for heat pumps and rooftop solar and a $27bn “clean energy technology accelerator” to help deploy new renewable technology.

A further $60bn would go towards environmental justice projects and there is a new program to reduce leaks of methane, a potent greenhouse gas, from oil and gas drilling.

“This will be, by far, the biggest climate action in human history,” said Brian Schatz, a Democratic senator from Hawaii. “The planet is on fire. Emissions reductions are the main thing. This is enormous progress. Let’s get it done.”

The authors of the bill predict it will cut US emissions by 40% by 2030, based on 2005 levels, a claim guardedly backed by independent experts. Scientists have said global emissions must be halved this decade then zeroed out by 2050 if the world is to avoid catastrophic heatwaves, droughts, floods and other climate impacts. Biden has set US emissions targets along these lines.

The bill would “bring clean energy jobs to America and lower energy bills for American families”, tweeted Leah Stokes, a climate policy expert at the University of California, Santa Barbara.

“It would get us 80% of the way to President Biden’s climate goal. This is a gamechanger.”

However, Manchin has said the legislation “does not arbitrarily shut off our abundant fossil fuels” and has extracted guarantees of new offshore and onshore drilling, including a stipulation that millions more acres of public lands be opened for fossil fuel companies before new solar or wind energy projects can do the same.

The West Virginia senator is a keen backer of a large proposed gas pipeline in his home state and has called for greater domestic oil production, citing fears over inflation.

The requirement for more drilling leases amounts to a “climate suicide pact”, according to Brett Hartl, government affairs director at the Center for Biological Diversity.

“The new leasing required in this bill will fan the flames of the climate disasters torching our country,” Hartl said, lamenting “a slap in the face to the communities fighting to protect themselves from filthy fossil fuels”.

Should the bill pass, it will almost certainly do so without a single Republican vote, with the party still almost uniformly opposed to any significant action to address the climate crisis or impinge on the fossil fuel industry.

Lindsey Graham, a Republican senator from South Carolina, said he could not believe that Manchin “is agreeing to a massive tax increase in the name of climate change when our economy is in a recession. I hope that common sense will eventually win the day.”