A Jeremy Corbyn supporter from north London stands to win £5,000 if, as expected, the left-wing MP becomes the new Labour leader on Saturday.
In the space of three months, Corbyn has gone from the rank outsider to the clear favourite in the Labour leadership race with his odds as high as 200/1 at the outset of the campaign.
Ladbrokes will pay out around £250,000 to people who backed Corbyn should he win, including one punter who put £50 on Corbyn when his odds were still at 100/1. Unless there is a shock result when the leader is announced on Saturday morning, he stands to win £5,000.
The gambler wanted to remain anonymous, but told BuzzFeed News he just "randomly decided" to put the bet on after becoming inspired by Corbyn's message.
"My instinct was that other people felt the same way as me: disillusioned with politics and politicians, turned off by soundbites and robot-like media training, and terrified by the worrying move of politics to the right," said the punter.
"I randomly decided to put a bet on, because a fellow supporter posted the Ladbrokes odds online, and I was in a pretty optimistic, hopeful mood. It felt like a risky bet, and a bit of wishful thinking (I don't generally make bets, and £50 is a lot), but I dared to hope for him to win, and went with it."
Gradually, as "Corbynmania" swept the nation, he watched Corbyn go from a token left-wing candidate to the man most likely to become Labour leader.
"When he made it on to the ballot, I started to get excited, but (genuinely) more for a compassionate future for the country – a saved NHS, greater equality – than the bet paying off," said the man. "I later went to my local CLP meeting and was overwhelmed when he won the room's nomination by a landslide."
The north London man has no grand plans for his winnings, saying he will pay off his debt and give some to charity.
"I'm not convinced he's definitely won yet," he said. "More than anything, I'm excited about the future of politics and democracy, but I will use some of the money to pay off the rest of my student loans (finally!).
"I also want to give money and time to help refugees. It feels right to help other people with my winnings."
A Ladbrokes spokesperson said the shift in Corbyn's odds is the biggest in political history.
"We will pay out around 250k to Corbyn backers but thanks to the record interest in the contest it only translates to a small loss," said the spokesperson.
"The shift in odds is the biggest in political betting history and one of the most unprecedented across all events and sports, full stop. It looks like being a genuine 'black swan' so we doff our caps to those who had the foresight.
"They may be getting a call from our recruitment department."