The two sides offered only basic details about the structure of the deal, called the United States-Ukraine Reinvestment Fund.
It is expected to give the US access to Ukraine's valuable rare earth minerals while providing Kyiv a measure of assurance about continued American support in its grinding war with Russia.
"This agreement signals clearly to Russia that the Trump administration is committed to a peace process centred on a free, sovereign and prosperous Ukraine over the long term," Treasury Secretary Scott Bessent said on Wednesday.
"President Trump envisioned this partnership between the American people and the Ukrainian people to show both sides' commitment to lasting peace and prosperity in Ukraine."
The announcement comes at a critical moment in the three-year war as Trump grows increasingly frustrated with both sides.
The signing comes two months after a different but similar agreement was derailed in a tense Oval Office meeting involving President Donald Trump, Vice-President JD Vance and Ukrainian President Volodymyr Zelenskiy.
Trump has long criticised Zelenskiy, saying he does not "have the cards" to win the war and blaming him for prolonging the killing by not giving up Crimea, but in recent days has also rebuked Russian President Vladimir Putin, saying he was complicating negotiations with "very bad timing" in launching deadly strikes on Kyiv.
Trump said the deal "in theory" meant the US would get more from Ukraine than it contributed.
"I wanted to be protected," he said on NewsNation, adding he did not want to look "foolish" by not getting money back for the investment.
For Ukraine, the agreement is considered key to ensuring its access to US military aid.
"This is truly an equal and good international deal on joint investment in the development and restoration of Ukraine between the governments of the United States and Ukraine," Prime Minister Denys Shmyhal said.
Ukraine's economy minister, Yulia Svyrydenko, flew to Washington to help finalise the deal.
"Together with the United States, we are creating the fund that will attract global investment to our country," she posted on X.
The US has sought access to more than 20 raw materials deemed strategically critical to its interests such as titanium, uranium and lithium, and non-minerals such as oil and natural gas.
Shmyhal said the deal would establish an equal partnership between the two countries and last 10 years.
The deal must be ratified by Ukraine's parliament before it can take effect.
The negotiations come amid rocky progress in Washington's push to stop the war.
Putin backs calls for a ceasefire before peace negotiations, "but before it's done, it's necessary to answer a few questions and sort out a few nuances", Kremlin spokesman Dmitry Peskov told reporters.
Putin was also ready for direct talks with Ukraine without preconditions, he said.
Trump has expressed frustration over the slow pace of peace negotiations, while European leaders accuse Putin of stalling while his forces seek to grab more Ukrainian land.
The US State Department on Tuesday tried again to push both sides to move more quickly and warned the US could pull out of talks if there was no progress.
The daily grind of the war shows no sign of letting up, with a night-time Russian drone attack on the Ukrainian city of Kharkiv wounding dozens of civilians.
