An independent commission will be created to investigate the January 6 riot at the US Capitol, House Speaker Nancy Pelosi said in a letter to politicians.
The outside investigation will be modelled on the inquiry that examined the 9/11 attacks of September 11, 2001.
Ms Pelosi said the investigation was needed to uphold US security after what she called the “domestic terror attack”.
The announcement comes on the heels of Republican senators acquitting President Donald Trump for his role in inciting the insurrection.
Only seven Republican senators voted to convict Mr Trump, with 43 others acquitting the former president, highlighting how powerful a grip he still has on the party.
Ms Pelosi condemned the “cowardly group of Republicans” for their actions.
Five people, including a Capitol police officer, died in or soon after the insurrection attempt by supporters of Mr Trump. Two other police officers involved in defending the building against the Trump-supporting mob later took their own lives.
Ms Pelosi called on Congress to allocate additional funding “to provide for the safety of members and the security of the Capitol”.
Her request to increase the Capitol’s security budget follows an investigation by retired US army lieutenant General Russel Honore, who was asked to assess security needs in the immediate aftermath of the attack.
“It is clear from his findings and from the impeachment trial that we must get to the truth of how this happened,” Ms Pelosi said.
Investigations into the riot were planned, with Senate hearings scheduled later this month.
An independent commission along the lines of the one that investigated the September 11 attacks would probably require legislation to create. That would elevate the investigation a step higher, offering a definitive government-backed account of events.
But such a panel would pose risks of sharpening partisan divisions or overshadowing President Joe Biden’s legislative agenda.
More than 200 people have been charged with federal crimes related to the insurrection attempt.
Many members of the pro-Trump mob used the app Parler to communicate online before the attack.
The app, which calls itself “the free speech social network”, was relaunched on Monday after it was forced offline over incitements to violence on the platform.
Parler, which says it has 20 million users, is popular among conservatives due to its lax regulation of hate speech and misinformation.
The app came under scrutiny following the Capitol attack, prompting Apple and Google to remove it from their download platforms. Amazon’s web-hosting service also cut its ties with the app.
Parler said it was back for users who had already installed it. New users won’t be able to gain access to it until next week.
