In remarks from the White House set for 11:40 a.m. EST, Obama will discuss executive action he is taking to require more gun sellers to get licenses and more gun buyers to undergo background checks.
He will be joined by people who have lost family members to gun violence, as well as gun owners who support the new measures.
Obama has often said his toughest time in office was grappling with the December 2012 massacre of 20 children and six adults at an elementary school in Newtown, Connecticut.
"The day that we traveled up to Newtown, two days after that massacre, was the worst day of his presidency. Just thinking about it makes me tear up," Valerie Jarrett, a senior adviser to Obama, said on MSNBC.
After that tragedy, the Democratic president failed to persuade Congress to toughen U.S. gun laws. He has blamed lawmakers for being in the thrall of the powerful National Rifle Association gun lobby group.
Subsequent mass shootings at a Charleston, South Carolina, church, a community college in Oregon, and the December shooting in San Bernardino, California by a couple inspired by Islamist militants have stiffened Obama's resolve to try to use his executive authority to do more to tighten access to guns.
Under the changes, the U.S. Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF) will issue guidelines intended to narrow exceptions to a system that requires sellers to check with the Federal Bureau of Investigation to determine whether buyers have criminal records, are charged with crimes or have mental health conditions that would bar them from owning a gun.
Any changes to gun rules in America are fraught with political risk. The U.S. Constitution's 2nd Amendment gives Americans the right to have arms, a right that is fiercely defended.
The stocks of gunmakers Smith & Wesson Holding Corp and Sturm Ruger & Co Inc have climbed since the announcement. On Tuesday morning, Smith & Wesson jumped 12.5 percent to $26.18 a share and Sturm Ruger was up 7.5 percent at $65.97.
Legal challenges to the changes are expected, and Republican presidential candidates have promised to reverse his order if they win the White House. But Obama, entering his eighth and last year in office, has said his measures are within his authority and consistent with the Constitution.