In 2019, the US House of Representatives voted through a recognition.
With today's announcement, Joe Biden follows up on the campaign promise he made a year ago.
He will be the first American president to publicly call the incident a genocide.
France and Russia, among others, have acknowledged the massacre as a genocide.
Turkey denies systematic killing
In 1915, about one million Armenians and other Christian minorities were killed in the then Ottoman Empire.
Turkey has acknowledged that many Armenians were killed in clashes with Ottoman forces during the First World War.
But the number of victims is questioned and it is denied that the killing was systematic.
It has been 106 years since the massacre began.
Victims around the world are now being noticed.
Biden's act is seen primarily as symbolic, but it involves a departure from decades of carefully balanced language from the White House.
May damage relations between countries
Some sources say that the issue is so sensitive that Biden may change at the last second so as not to ignite the conflict with NATO colleague Turkey.
The governments of Ankara and Washington have already disagreed on a number of issues, and Turkish Foreign Minister Mevlüt Cavusoglu warned Biden this week that a genocide statement would further damage relations between the two countries.