Fourteen other people were injured, while the gunman, identified as Aaron Alexis, 34, of Fort Worth, Texas, was later killed in a gun battle with security at the sprawling Washington Navy Yard complex in Southeast Washington not too far from the Capitol and the White House.
Vishnu Pandit, an Indian origin man, was identified Monday night along with six other victims: Michael Arnold, 59; Sylvia Frasier, 53; Kathy Gaarde, 62; John Roger Johnson, 73; Frank Kohler, 50; and Kenneth Bernard Proctor, 46.
61-year-old Indian American Vishnu Pandit was among 13 killed in mass shooting.
No further details were available about the victims.
Alexis who received a general discharge in 2011 from the Navy Reserve, was arrested but not charged in a gun incident in Seattle in back 2004 but still had a security clearance with a military contractor that would have allowed him access to the Navy Yard, officials said.
Even as the Federal Bureau of Investigation (FBI) ruled out any other shooters in the rampage at the headquarters for Naval Sea Systems Command, Washington Metropolitan Police were trying to track down at least one person to determine whether that individual had any involvement.
"We'll continue to seek information about what the motive is. We don't have any reason at this stage to suspect terrorism," Washington Mayor Vincent Gray told reporters, adding, "but certainly it has not been ruled out".
The other possible suspect was described by police as a black male, between 40 and 50, wearing an "olive drab-coloured" military-style uniform.
President Barack Obama called the shooting a "cowardly act" that targeted military and civilians serving their country and vowed that federal and local law enforcement officials would work together to hold accountable those responsible for the shooting.
"They know the dangers of serving abroad," he said, "but today they faced the unimaginable violence that we wouldn't have expected here at home."
The worst shooting incident at a military installation since 13 people were killed at Fort Hood, Texas, in 2009 began unfolding at 8.20 a.m. when several shots were fired inside the southeast Washington facility, where some 3,000 military and civilian employees work.
Police described the alleged suspect as an adult male, about six feet tall with a bald head and medium complexion, dressed in a black top and black jeans.
He was armed with a semi-automatic AR-15 rifle, another rifle and a semi-automatic Glock handgun.
The injured included a Washington police officer who has been hospitalised, and a base security guard officer, according to police.
Air traffic to Reagan National Airport was briefly suspended after the shooting and 10 public and charter schools and a public school administration building in the capital were also placed on lockdown as a precaution.
Officials postponed a Washington Nationals baseball game that had been scheduled for Monday night at Nationals Park, just a few blocks away from the Washington Navy Yard, US Navy's oldest land establishment created in 1799.