The law firm of Davidoff Hutcher & Citron filed suit against Bannon in February, alleging the "War Room" podcaster owed them $480,487.87 in unpaid fees for their work in numerous legal matters, including two federal criminal cases and a subpoena from the House committee that was investigating the Jan. 6, 2021, riot at the U.S. Capitol.
The firm started representing Bannon in November 2020, after he was indicted in federal court in New York for allegedly taking part in a scheme to defraud donors who wanted to build a wall along the southern U.S. border.
Bannon's co-defendants were convicted, but he never stood trial in that case because he was pardoned by Trump in the final hours of his presidency.
The presidential pardon "was secured through the aid of DHC," the firm said in its lawsuit.
Bannon has since been hit with charges related to the fraud allegations by the Manhattan district attorney's office. He's scheduled to stand trial next May.
The firm also represented Bannon when he snubbed a subpoena from the Jan. 6 committee, which eventually led to his being convicted of criminal contempt of Congress. He was sentenced to four months behind bars, but the sentence was stayed while he appeals the conviction.
The firm said that it did legal work for Bannon until November 2022, and that he paid only about $375,000 out of the more than $850,000 he'd been billed.
Bannon said he told the firm to "stop working on his behalf in January 2022," a claim the firm denied.
In a ruling Friday, Justice Arlene Bluth sided with the law firm, saying it had shown that Bannon "was actively seeking" their legal representation "well after the time (January 2022) that defendant allegedly told plaintiff to stop providing legal services," and that Bannon never objected to any of their invoices.
Bannon's current lawyer, Harlan Protass, told NBC News, "The judge's decision was clearly wrong and we intend to immediately appeal."
An attorney for Davidoff Hutcher & Citron did not immediately respond to a request for comment.