Steve Bannon, a former political adviser of US President Donald Trump, pleaded not guilty to fraud charges in federal court on Thursday.
Bannon and three other leaders of the "We Built the Wall" online fundraising campaign were arrested and charged with defrauding hundreds of thousands of donors.
The campaign raised more than $25 million (€21.1 million).
All four men appeared in front of judges on Thursday. They were each charged with one count of conspiracy to commit wire fraud and one count of conspiracy to commit money laundering, each of which carries a maximum jail sentence of 20 years.
Appearing at his hearing, Bannon had his hands cuffed in front of him while a large, white mask covered most of his face.
Inspector-in-Charge Philip R. Bartlett said in a statement that "the defendants allegedly engaged in fraud when they misrepresented the true use of donated funds."
"As alleged, not only did they lie to donors, they schemed to hide their misappropriation of funds by creating sham invoices and accounts to launder donations and cover up their crimes, showing no regard for the law or the truth," he added.
According to prosecutors, Bannon, 66, received $1 million (€840,000) from the online fundraising campaign through a non-profit organisation under his control, hundreds of thousands of which were used to cover his personal expenses.
Another of the defendants, Brian Kolfage, a 38-year-old US Air Force veteran, also received $350,000 in funds for his personal use.
The indictment noted that the defendants had repeatedly assured donors that 100 per cent of the donated funds would go towards the construction of the wall.
Bannon was appointed chair of Trump's presidential campaign — in which building a wall along the border with Mexico was a key pledge — in August 2016 and served in the administration as an advisor to the president until August 2017.
Prior to these roles, Bannon founded and ran Breitbart News, a conservative news site, and also co-founded Cambridge Analytica, a British political consulting firm which was later found to have illegally acquired the personal data of millions of Facebook users.
After he was pushed out from the White House, Bannon set his sights on Europe where he hoped to facilitate a rise in far-right politics but failed to gather sufficient momentum for his movement.