Anthime "Tim" Gionet, 34, also admitted in an "statement of offence" filed with his guilty plea to being part of the mob that entered the Capitol without authorisation and occupied the building for hours.
The riot on January 6, 2021, left more than 140 police officers injured and disrupted congressional certification of the November 2020 presidential election victory of Democrat Joe Biden over Trump, who led Republicans in falsely claiming he lost due to widespread fraud.
The attack on the Capitol also led to several deaths.
Gionet, a banned YouTube prankster and former BuzzFeed social media strategist calling himself Baked Alaska, pleaded guilty on Friday in US District Court for the District of Columbia to one count of unlawfully "parading, demonstrating or picketing in a Capitol building".
The misdemeanour offence carries a maximum sentence of six months in prison and a fine up to $US5000 ($A7200). Sentencing was set for January 12. He remains free on personal recognisance.
In his statement, Gionet acknowledged egging on other rioters to "come in" and "make yourself at home", as well as live-streaming the event for 27 minutes and joining in various chants.
Gionet also filmed himself pretending to make a call from a Senate conference room and propped his feet up on a table in another Senate office, admonishing others "not to break anything" before eventually being ushered to an exit by law enforcement whom he cursed as "oath-breakers".
More than 850 people have been charged with taking part in the riot, with more than 325 guilty pleas so far.
