Predecessors who did not wish to antagonise Turkey, a North Atlantic Treaty Organisation ally and a strategically pivotal country straddling Europe and the Middle East.
Biden said his statement was "not to cast blame but to ensure that what happened is never repeated".
Biden, who took office in January vowing a new focus on human rights, spoke for the first time as president with his counterpart Recep Tayyip Erdogan yesterday on the eve of the expected announcement.
Erdogan, in a statement to the Armenian patriarch in Istanbul, said that debates "should be held by historians" and not "politicized by third parties".
Biden has established a pattern of calling world leaders to warn them of forthcoming moves by his administration which will irritate the relationship.
Erdogan on Thursday told advisors to "defend the truth against those who back the so-called "Armenian genocide" lie", with his foreign minister warning that the United States would set back relations. It says numerous victims were casualties of the war or murdered by Russians.
Turkey accepts that many Armenians living in the Ottoman Empire were killed in clashes with Ottoman forces during World War One, but contests the figures and denies the killings were systematically orchestrated and constitute a genocide.
"For millions of Armenians these wounds are still wide open".
He voiced hope for greater USA alignment against Turkish-backed Azerbaijan, which past year won back swathes of territory controlled by Armenia since a war in the 1990s.
The much anticipated phone call took place more than three months after Biden's January 20 inauguration, a delay that is widely seen as a cold shoulder to Erdogan, who had enjoyed close ties with former President Donald Trump.
But in a potential sign that the two leaders want to avoid further deterioration of relations, the White House said that Biden and Erdogan would meet when they are in Brussels in June for a North Atlantic Treaty Organisation summit.
A Turkish statement on the call similarly stressed the positive, saying Erdogan and Biden agreed on "the importance of working together".
"We wanted it before Biden", she told AFP.
"This principled stand represents a powerful setback to Turkey's century-long obstruction of justice for this crime, and its ongoing hostility and aggression against the Armenian people", he said.
Biden's declaration follows a non-binding resolution by the U.S. Senate adopted unanimously in 2019 recognizing the killings as genocide.
"Turkey will raise a rhetorical fuss for a few days and perhaps delay acting on some routine requests from the USA military". In recent years, Turkey has launched military operations against PKK enclaves in Turkey and in northern Iraq and against US-allied Syrian Kurdish fighters.
Biden before taking office called Erdogan an autocrat and voiced support for Turkey's opposition.
Turkey has also infuriated much of the U.S. political establishment with its incursions against US-allied Kurdish fighters in Syria who helped fight the Islamic State group but are linked to militants inside Turkey. His administration has also criticised homophobic statements from those close to Erdogan.