People fled the complex by scrambling down scaffolding erected for renovations, while others took cover inside as police with rifles and body armor took up positions outside and cordoned off the normally bustling streets around Parliament.
At least three people were treated for minor injuries.
In Washington, President Barack Obama condemned the shootings as "outrageous" and said: "We have to remain vigilant." The U.S. Embassy in Ottawa was locked down as a precaution, and security was tightened at the Tomb of the Unknown Soldier at Arlington National Cemetery just outside Washington.
Harper vowed that the attacks will "lead us to strengthen our resolve and redouble our efforts" to keep the country safe and work with Canada’s allies to fight terrorists.
Court records that appear to be the gunman’s show that he had a long rap sheet, with a string of convictions for assault, robbery, drug and weapons offenses, and other crimes.
The Canadian Broadcasting Corp. had video of the gunman going to his car alone with his weapon after the shooting at the memorial. The car was later spotted parked in front of Parliament Hill, just down the block.
Parliament remained under close surveillance by police and was closed to the public. Security was beefed up at government buildings across Canada. The federal government confirmed Tuesday it had raised its threat level due to an increase in "general chatter from radical Islamist organizations."