A jury convicted Roger Stone on Friday on all seven counts of lying to Congress, obstruction and witness tampering in a federal indictment.
The trial, which emerged from former special counsel Robert Mueller's investigation into Russian meddling in the 2016 US presidential election, highlighted how Trump associates gathered information about hacked emails released by WikiLeaks and damaging to his Democratic rival, Hillary Clinton.
The 67-year-old Stone denied wrongdoing and criticized the case as being politically motivated.
Stone did not testify during the trial and his lawyers did not call any witnesses in his defense. He is expected to be sentenced on February 6 next year and could face up to 20 years in prison.
Steve Bannon, who was the Trump campaign's CEO and later served as White House chief strategist, testified that Stone had bragged about his connections to WikiLeaks and its founder, Julian Assange, having alerted them to new incoming emails that were potentially dangerous.
Asked whether he had any comments on the verdict after leaving the courtroom, Stone told reporters, "None whatsoever," according to news agency AP.
Stone is the latest in a group of former Trump advisers to be convicted of lying to authorities, including: Paul Manafort, a former Trump campaign chairman; Rick Gates, Trump's deputy campaign head; Michael Flynn, a former national security adviser; Michael Cohen, Trump's personal lawyer; and George Papadopoulos, a former campaign aide.
Trump's reaction
Friday's verdict intensifies scrutiny on Trump as he faces an impeachment inquiry.
Trump tweeted minutes after the verdict, calling the conviction "a double standard like never seen before in the history of our country,'' and accusing Clinton and Mueller of lying.