The former secretary of state, New York senator and first lady has reached the 2,383 delegates needed to become the presumptive Democratic nominee, according to an Associated Press count.
She had a decisive weekend victory in Puerto Rico and a burst of last-minute support from superdelegates, who are party officials and officeholders. Many of them are eager to wrap up the contest amid polls showing her in a tightening race with presumptive Republican nominee Donald Trump.
Mrs Clinton has 1,812 pledged delegates won in primaries and caucuses. She also has the support of 571 superdelegates, according to AP.
The AP surveyed all 714 superdelegates repeatedly in the past seven months, and only 95 remain publicly uncommitted.
While superdelegates will not formally cast their votes for Mrs Clinton until the party’s July convention in Philadelphia, all those counted in her tally have unequivocally told AP they will do so.
“We really need to bring a close to this primary process and get on to defeating Donald Trump,” said Nancy Worley, a superdelegate who chairs Alabama’s Democratic Party and provided one of the last endorsements to put Mrs Clinton over the top.
The victory arrived eight years after she conceded her first White House campaign to Barack Obama.
Back then, she famously noted her inability to “shatter that highest, hardest glass ceiling”.
Campaigning this time as the loyal successor to the nation’s first black president, Mrs Clinton held off a surprisingly strong challenge from Vermont senator Bernie Sanders.
He mobilised millions with a fervently liberal message and his insurgent candidacy revealed a deep level of national frustration with politics-as-usual, even among Democrats who have controlled the White House since 2009.
Clinton greeted news of her achievement with a measured response, wary of depressing turnout and eager to save the revelry for a big victory party last night in Brooklyn.
“We’re going to fight hard for every single vote,” Clinton declared.
Clinton has been eager to move past the protracted primary and fully turn her attention to her general election battle with Trump.
She energised Democrats with a blistering speech last week challenging Trump’s qualifications for the presidency, telling supporters that she’s prepared for a bruising campaign against the businessman.