Bannon, 68, was convicted in July on two counts – for refusing to provide either testimony or documents to a committee probing the 6 January 2021 riot at the US Capitol.
In addition to the jail time, Bannon must also now pay a fine of $6,500 (£5,833).
He has denied any criminal wrongdoing.
Judge Carl Nichols said that Bannon would be released for the time being, while any appeal to the sentence is resolved.
“Today was my judgement day by the judge,” Bannon told reporters immediately following the sentencing. “We will have a vigorous appeal.”
Referring to the upcoming midterm elections, he added: “On 8 November we are going to have judgement on the illegitimate Biden regime.” Bannon has repeatedly made similar statements in the past and falsely claimed that Donald Trump won the 2020 presidential election.
Hours after Bannon was sentenced, Mr Trump was formally issued his own legal summons from the 6 January panel, ordering him to testify before lawmakers about the Capitol riot.
Like Bannon, Mr Trump could face criminal charges if he does not comply with the summons.