Prosecutors had asked US District Judge Royce Lamberth to impose a longer 51-month sentence on Jacob Chansley, who pleaded guilty in September to obstructing an official proceeding when he and thousands of others stormed the building in an attempt to stop Congress from certifying President Joe Biden's election.
The sentence matches one imposed by a judge on a former mixed martial artist filmed punching a police officer during violence, who was sentenced last week to 41 months in prison.
Lamberth said he believed Chansley, who made a lengthy speech before he was sentenced, had done a lot to convince the court he is "on the right track".
Chansley's lawyers asked the judge for a sentence of time served for their client, who has been detained since his January arrest.
He appeared in court in a dark green prison jumpsuit, with a beard and shaved head.
While in detention, Chansley was diagnosed by prison officials with transient schizophrenia, bipolar disorder, depression and anxiety.
When he entered his guilty plea, Chansley said he was disappointed Trump had not pardoned him.
Trump was impeached by the House of Representatives and acquitted by the Senate on a charge of inciting the January 6 riot for a fiery speech that preceded it.
Four people died in the violence.
A Capitol Police officer who had been attacked by protesters died the day after the riot and four police officers who took part in the defence of the Capitol later took their own lives.
About 140 police officers were injured.
Defence lawyer Albert Watkins said the US navy in 2006 had concluded Chansley suffered from personality disorder but nonetheless declared him "fit for duty".
