Both Capitol Police officers were taken to the hospital, with one having "succumbed to his injuries", Capitol Police Acting Chief Yogananda Pittman told reporters.
The statement came after a motorist, reportedly identified as Noah Green, plowed a auto into a barrier at the Capitol.
A photo taken by an Associated Press photographer showed officers surrounding a vehicle that appeared to have crashed into a barricade on the Capitol's north side.
During a news conference, U.S. Capitol Police Acting Chief Yogananda Pittman said the auto rammed the two officers at what police call the north barrier, located at DE and Constitution avenues, then the driver got out and lunged at officers with a knife in his hand. He had been a member of the U.S. Capitol Police for 18 years.
Two law enforcement sources involved in the investigation told BBC partner CBS News that the suspect in the attack was 25-year-old Noah Greene from Indiana.
Vice President Harris condemned the attack at the Capitol Friday that killed one police officer and wounded another, calling it "inexplicable".
"The man exited the vehicle with a knife and ran toward our officers".
The officers opened fire and the suspect was shot dead.
Police said the suspect died due to his injuries at 13:30 local time.
According to the Capitol Police, the second officer is in stable and non-threatening condition. "All three have been transported to the hospital".
Acting Metropolitan Police Chief Robert Contee said the investigation into the incident was ongoing. "But obviously, we'll continue to investigate to see if there is some type of nexus along those lines", he said at a news conference Friday.
U.S. Capitol Police officers stand near a auto that crashed into a barrier on Capitol Hill in Washington, D.C., Friday.
Video shared on social media also showed a helicopter landing at the Capitol. The White House said the president has been briefed on the situation. Also House Speaker Nancy Pelosi ordered the flags at the US Capitol to be flown at half-staff due to the death of the police officer, Pelosi's deputy chief of staff tweeted.
The incident follows recent ramping down of some additional protective measures that were put into place after the January 6 insurrection at the Capitol Hill complex.
"I want to express the nation's gratitude to the Capitol Police, the National Guard Immediate Response Force, and others who quickly responded to this attack", Biden said. Since the riot on 6 January, the complex has been like a fortress with barbed wire, metal fencing and heightened security.