"The president is going to act," the vice-president, who's heading a task force on gun control for his boss, said before meeting with gun control advocates and victims of gun violence.
"There are executive orders, executive action that can be taken. We haven't decided what that is yet, but we're compiling it all."
Last month's horrifying mass shooting in Newtown, Conn., which claimed the lives of 20 six- and seven-year-olds, has necessitated "immediate, urgent action," Biden added.
The massacre of those Grade One pupils with a legally purchased, high-powered rifle has affected Americans "in a way like nothing I've seen in my career," he said.
Colin Goddard, who was shot four times in the 2007 Virginia Tech massacre, was among those meeting with Biden on Wednesday.
"My job is to represent the voice of the overwhelming majority of Americans ... that want some comprehensive, common-sense changes to our gun policy," said Goddard, who now works for the Brady Campaign to Prevent Gun Violence.
In the wake of Biden's warning, however, gun rights activists still have reason to breathe easy — there's scant action available to the Obama administration without Congress.
Obama and Democrats are pushing for the reinstatement of an assault weapons ban.
The White House would also like to see measures that include mandating universal background checks for firearm buyers, tracking the movement and sale of weapons through a national database, beefing up mental health checks and toughening penalties for carrying guns near schools or giving them to minors.
For almost all of those measures, the president needs lawmakers behind him.
Executive orders would only allow Obama to make changes to federal mental health programs and to modernize gun-tracking efforts by the Bureau of Alcohol, Tobacco, Firearms and Explosives.
He might also be able to push through initiatives to track the mental illness histories of gun-owners and to implement more information-sharing between and state and local law enforcement agencies.
On Thursday, Biden meets with representatives of the powerful National Rifle Association, the country's biggest gun rights lobby.
The NRA's deep pockets have long served to persuade members of Congress to oppose gun control bills.
Earlier this week, Gabrielle Giffords, the former Arizona congresswoman shot in the head by a would-be assassin two years ago, unveiled a new group aimed at countering the NRA.
Obama hopes to announce his administration's gun reform measures shortly after his inauguration on Jan. 21.
The inaugural weekend festivities might be disrupted by a coalition of conservative and gun-rights groups organizing a "Gun Appreciation Day" on the weekend of the inauguration. The group is calling on people to visit gun stores, gun ranges and gun shows with U.S. flags and "Hands off my gun" signs.
A longtime advocate of gun control himself during his three decades as a senator, Biden's remarks on Wednesday set off an immediate firestorm among gun rights activists, with the right-wing Drudge Report even comparing Obama to Adolf Hitler and Joseph Stalin.
Gun rights advocates often assert that Nazi Germany banned guns before embarking upon the Second World War and the Holocaust. Several of them have made the allegation while appearing on various news shows in the aftermath of the Newtown shooting.
But in fact, Hitler loosened gun laws in 1938 so that German citizens —although not Jews or supposed enemies of the state — could buy handguns with simple hunters' permits.