Darren Grimes, 25, was fined in 2018 after being accused of breaching spending rules during the EU referendum campaign.
But he insisted he was ‘completely innocent’ of making false declarations in relation to a £680,000 donation to his BeLeave group from the main Vote Leave campaign.
The Electoral Commission found that BeLeave spent more than £675,000 with Canadian data firm Aggregate IQ under a plan with Vote Leave, which should have been declared.
This spending took Vote Leave over its £7 million legal spending limit by almost £500,000.
Mr Grimes raised £93,956 via an online crowdfunding campaign to appeal against the verdict of the commission at the Mayor’s and City of London Court in Central London.
He had said that he had intended to register the organisation BeLeave and not himself as an individual on the forms.
His lawyers said he had filled out the complex and difficult-to-understand forms to the best of his ability.
The judge said Mr Grimes had tried to meet his obligations to the commission in filling out the forms, and that his actions were not dishonest or lacking transparency.
Following the ruling Mr Grimes said: ‘I am delighted and relieved that the court has found me innocent.
‘This case has taken a huge toll on myself and my family, and I’m thankful it’s now over. I will be eternally grateful to all those people who have supported me – your generosity and kind words of encouragement have kept me going.’
In the message, posted on Twitter, he hit out at the watchdog’s handling of the case.
He said: ‘The Electoral Commission’s case was based on an incorrectly ticked box on an application form – something that it had been aware of for over two years and had not been raised in two previous investigations.
‘Yet the Commission still saw fit to issue an excessive fine and to spend almost half a million in taxpayer cash pursuing me through the courts. This raises serious questions about its conduct both during and after the referendum.
‘It’s vital that more young people are encouraged to get involved in politics and make their voices heard.’
The Electoral Commission said it was ‘disappointed’ Mr Grimes’ appeal was upheld and will ‘review the full detail of the judgment before deciding on next steps, including any appeal.’
Judge Marc Dight’s ruling means that the order against Mr Grimes will be quashed and the commission will have to pay his costs, according to Mr Grimes’s lawyer, Timothy Straker QC.
The amount of the costs still has to be assessed.