Stewart Rhodes, founder of the US far-right group Oath Keepers, and his associate Kelly Meggs were found guilty by a jury of seditious conspiracy and other charges for crimes related to the Capitol Hill riot on January 6, 2021.
Their actions disrupted a joint session of Congress that was in the process of ascertaining and counting the electoral votes related to the 2020 presidential election, reports Xinhua news agency.
Three additional defendants, who were leaders and associates of the organisation, were also found guilty on Tuesday of related felony charges.
The verdicts followed an eight-week trial and three days of deliberations.
No sentencing date was set.
Rhodes, 57, of Granbury, Texas, was found guilty of obstruction of an official proceeding and tampering with documents and proceedings.
Meggs, 53, of Dunnellon, Florida, was found guilty of conspiracy to obstruct an official proceeding, obstruction of an official proceeding, conspiracy to prevent an officer from discharging duties, and tampering with documents or proceedings.
According to the Department of Justice, the Oath Keepers is a large but loosely organised collection of individuals, some of whom are associated with militias.
Following the November 3, 2020, presidential election, Rhodes, Meggs, and others began plotting to oppose by force the transfer of presidential power, court documents showed.
In the 22 months since the riot, over 900 individuals have been arrested in nearly all 50 states for crimes related to the breach of theCapitol, including over 275 individuals charged with assaulting or impeding law enforcement.