The donation gives the veteran Brexit campaigner's party £72 million ($A136 million) from two donors in less than 48 hours at a time when it is confronting allegations about irregularities in its funding, which it denies.
The figure exceeds what either the governing Labour Party or the opposition Conservatives spent during last year's election campaign, according to Electoral Commission figures.
The funds will help Reform, whose lead in opinion polls has slipped over the funding allegations, win over voters before the next election, which is due by 2029.
Harborne, already Reform's biggest donor, disclosed the contribution in a Telegraph newspaper article, saying fellow crypto investor Ben Delo's pledge a day earlier had inspired him to match it.
"What do I expect in return for my donations? Nothing. No peerage, no policy change, just a party that is ready for government," Harborne wrote in the article.
Delo's donation on Friday had already dwarfed the previous record of £10 million ($A19 million) that British businessman John Sainsbury, who died in 2022, had left to the Conservatives, according to the Electoral Commission's online database.
Reform has said that if it comes to power, it would propose a law to boost crypto adoption, including by cutting capital gains tax for digital assets and creating a bitcoin reserve fund at the Bank of England.
The donation comes little more than a week after Reform was hit by allegations that two senior aides to Farage had helped arrange for a foreign donor to fund political polling, claims which the party denies.
Earlier in September, Reform said head of policy James Orr and Farage adviser Dan Jukes had stepped down pending an internal investigation after an undercover investigation broadcast by Channel 4 alleged the party had broken electoral law by arranging for a US company to pay for polling commissioned by the party.
Reform has denied any wrongdoing, saying it had been targeted in a hoax by climate activists. Farage has said the party had "broken no laws" and had not taken any improper donations.
Labour has asked police to investigate possible offences linked to the allegations.
Police said they were assessing information provided to them, while the Electoral Commission said it was considering the claims and was in contact with law enforcement.
On Friday, Delo, the British co-founder of cryptocurrency trading platform BitMEX who was convicted of a US Bank Secrecy Act violation and later pardoned by President Donald Trump, said he would donate £36 million ($A68 million) to Reform.
Delo said he wanted the party to spend less time fundraising and more time preparing for government, arguing it needed resources to compete with Britain's two established parties, Labour and the Conservatives.
Farage welcomed the backing from both men on Saturday.
"I am honoured and humbled that Ben Delo and Christopher Harborne have shown such confidence in Reform," he said in a statement.
"Both men know that we are the only party that can turn the country around and win the next general election. Thanks to their generosity, we are now able to fight that election on a level playing field."
