Biden and Harris will start their day with a visit to the New York City site where planes brought down the World Trade Center's twin towers.
Harris, now the Democratic nominee for president, was due to travel to New York after debating her Republican rival, former president Donald Trump, in Philadelphia on Tuesday evening, with eight weeks left before the November 5 presidential election.
No remarks are scheduled at the site on Wednesday, where relatives will read the names of those who died.
Trump said he would attend the New York City ceremony along with his running mate JD Vance.
Former New York mayor Michael Bloomberg would also attend, a source familiar with the plans said.
Biden and Harris will then fly to Shanksville, Pennsylvania, where passengers on United Flight 93 overcame the hijackers and the plane crashed in a field, preventing another target being hit.Â
Then they will head back to the Washington area to visit the Pentagon memorial.
"We can only imagine the heartbreak and the pain that the 9/11 families and survivors have felt every day for the past 23 years and we will always remember and honour those who were stolen from us way too soon," White House spokeswoman Karine Jean-Pierre told reporters aboard Air Force One on Tuesday.
"We will continue to do everything in our power to ensure that an attack like this never happens again."
Biden issued a proclamation honouring those who died as a result of the attacks, as well as the hundreds of thousands of Americans who volunteered for military service afterwards.
"We owe these patriots of the 9/11 Generation a debt of gratitude that we can never fully repay," Biden said, citing deployments to Afghanistan, Iraq and other war zones, as well as the capture and killing of September 11 mastermind Osama bin Laden and his deputy.
US congressional leaders on Tuesday posthumously awarded the congressional gold medal to 13 of those service members who were killed in the August 26, 2021, suicide bombing at Kabul's airport during the chaotic US withdrawal from Afghanistan.
