Trump "needs to be exonerated," said the former White House chief strategist, who also formerly ran the Breitbart News far-right media outlet. "I don't think Trump will look for simple acquittal. He'll want to be exonerated."
The House Judiciary Committee has taken the first steps toward voting on two articles of impeachment introduced by Democrats. Trump is being charged with abuse of power for asking Ukraine to investigate former Vice President Joe Biden while withholding aid as leverage, and with obstruction of Congress for stonewalling the House investigation.
Bannon blasted the impeachment inquiry, labeling it a "show trial," saying the high-level July phone call between Trump and Ukraine's leader is what the president was "hired to do."
Trump "believes, and I think his followers believe, and now all of the Republican Party believes that what he did was correct," Bannon added in a "Squawk Box" interview.
The House is expected to vote on the impeachment articles next week, in the days before Christmas. That would send them to the Republican-held Senate for a 2020 trial.
Bannon sees a Senate trial as a "foregone conclusion" in the president's favor.
The White House did not immediately respond to CNBC's request for comment. Though Trump Press Secretary Stephanie Grisham, speaking to The Washington Post, said she expects the president to be exonerated.
"The president will address these false charges in the Senate and expects to be fully exonerated, because he did nothing wrong," said Grisham after the two impeachment articles were announced.
— The Associated Press contributed to this report.