A female civilian bystander was injured by shrapnel, but no U.S. Capitol Police officers were injured.
"We believe this is an act of a single person who has frequented the Capitol grounds before, and there is no reason to believe this is anything more than a criminal act," U.S. Capitol Police Chief Matthew Verderosa said.
Police said the suspect, Larry Russell Dawson, faces charges of assault with a deadly weapon and assault on a police officer while armed. He underwent surgery and was in stable but critical condition Monday.
Once released from the hospital, the 66-year-old will be presented to the District of Columbia Superior Court, U.S. Capitol Police said.
The police chief described the woman's injuries as "minor" and said she was taken to a hospital.
The suspect attempted to go through the metal detectors at the Capitol Visitor Center entrance. When those magnetometers beeped, he was stopped by security and then pulled out what appears to be a weapon. A Capitol police officer then shot him, sources told CNN.
Verderosa said an object that appeared to be a weapon was recovered on the scene.
Dawson was arrested on a charge of assaulting a police officer in October after an outburst in the chamber of the House of Representatives. Court documents from that 2015 incident describe Dawson as a 66-year-old man from Tennessee. In that incident, the documents state, Dawson "loudly stated to Congress he was a 'prophet of God.' "
The Capitol complex was locked down for nearly an hour following the incident. The Senate sergeant at arms has told staffers and others to "return to normal operations."
"Per USCP, shelter in place has been lifted and the Capitol is open for official business only. Capitol Visitor Center remains closed," the Senate sergeant at arms tweeted.
There were no other suspects involved, according to a notice sent to Senate staffers.
"There has been an isolated incident at the U.S. Capitol. There is no active threat to the public," the D.C. Police Department tweeted.
Police and firefighters swarmed the entrance of the visitor center, which is packed this week with tourists, spring break visitors and school groups.
Congressional staffers were sent a notice to shelter in place, instructing them to lock doors and move to assigned shelter areas. Those outside the buildings on the Capitol complex were told to "seek cover away from the area."
Most lawmakers were away from the Capitol on Monday.
House Speaker Paul Ryan, who is not currently in Washington, has been briefed on the incident, according to his spokesman.
"Today we are reminded of the courage and daily sacrifice of the United States Capitol Police," he said in a statement. "The Capitol is our greatest symbol of democracy, and these officers serve to protect not just those who work there but also the millions of visitors from all around the world who travel each year to see it."
Senate Majority Leader Mitch McConnell is in Louisville and his staff is safe, his spokesman said.
The White House also briefly closed its North and South fence lines as a precautionary measure after the Capitol incident.