Biden honoured the service and sacrifice of US military veterans, including those who paid the ultimate price, and their families, during what was his final time speaking at the cemetery's memorial amphitheatre in his capacity as commander in chief of the US military.
"It's been the greatest honour of my life, to lead you, to serve you, to care for you, to defend you, just as you defended us, generation after generation after generation," Biden said.
"You are the greatest fighting force, and this is not hyperbole, the finest fighting force in the history of the world."
He reminisced about trips to US military installations around the world, and to such historical military sites as Valley Forge and Gettysburg in Pennsylvania.
Joe Biden and Kamala Harris wore solemn expressions at the Tomb of the Unknown Soldier. (AP PHOTO)
Biden also announced that the Department of Veterans Affairs is expanding the types of cancers covered under the PACT Act, legislation he signed to expand health care services for veterans who served at military bases where toxic smoke billowed from "burn pits".
More than a million veterans and families have been helped under the law, he said.
The president opened his brief remarks by stating that the United States' "truly sacred obligation" is to prepare those it sends into harm's way and care for them when they come home, or don't.
"To all the military families, to all those with a loved one still missing or unaccounted for, to all Americans grieving the loss of a loved one who wore the uniform, Jill and I want you to know we see you, we thank you and we'll never stop working to meet our sacred obligation to you and your family," he said.
Biden's son Beau, who Jill helped raise, served in the Delaware Army National Guard and deployed to Iraq in 2008 for about a year.
He died of brain cancer in 2015 at the age of 46.
Biden and Harris, accompanied by Veterans Affairs Secretary Denis McDonough, wore solemn expressions on their faces as they approached the tomb.
They placed their hands over their hearts as the national anthem played before the wreath-laying, and again afterward as Taps sounded.
The president and first lady Jill Biden had hosted veterans and members of the military community at the White House before they and Harris and her husband, Doug Emhoff, departed for the hallowed burial ground across the Potomac River from Washington DC.
It was the first time that Biden and Harris had been seen together in public since the vice president lost last week's election to former president Donald Trump.
Before leaving the cemetery, Harris and Emhoff visited a gravesite.
The White House did not say who is buried there.
After the observance, Biden was travelling home to Wilmington, Delaware, for reasons the White House had yet to disclose.
