After the arrest, Riverside County Sheriff Chad Bianco said in a press conference and media interviews that deputies who prevented Vem Miller from entering the event in Coachella over the weekend "probably" stopped a "third assassination attempt."
Miller denies those claims. The 49-year-old, who is believed to be associated with a "Sovereign Citizens" group, has since been released on bail.
The lawsuit argues that Bianco fabricated the allegations in order to "create a narrative so as to be viewed as a 'heroic' Sheriff who saved Presidential candidate Trump from a third assassination attempt."
Man arrested near SoCal Trump rally denies intent to harm former president
"Even after being notified by both United States Secret Service and Federal Bureau of Investigation that they did not believe Miller was a threat and declined to interview him, Defendant Bianco continued to make preposterous allegations against Miller, holding press conferences perpetuating his delusional and false narrative," the lawsuit said.
Miller was released on $5,000 bond on Saturday following his arrest for misdemeanor gun charges after authorities said they found a shotgun, loaded handgun and a high-capacity magazine in his car outside the rally.
Miller claims he had the guns for protection, and said he forgot about California's gun laws. He also said he's a Trump supporter who was at the rally as a special guest.
Miller further argued in his lawsuit that Bianco lied when he told reporters Miller presented a fake VIP and press passes as he sought to gain entry to Trump's rally, when Miller says he "was actually provided expedited special entry passes by the Trump 47 campaign directly."
Bianco did not immediately respond to a request for comment from ABC News.
Trump, meanwhile, has not commented publicly about the arrest.