The former secretary of state has become first woman in the history of American politics to secure delegates necessary to clinch the Democratic nomination.
"We made history tonight-but we have more work to do. Chip in if you've got Hillary's back," said Hillary Clinton.
She claimed the Democratic presidential nomination on Tuesday night after decisive victories in the New Jersey and New Mexico primaries.
After claiming victories she appealed to supporters of Senator Bernie Sanders of Vermont to unite with her against Donald J. Trump.
New York tabloid Daily News changed its front page in honour of Clinton.
Clinton's nomination would mark a U-turn from a political culture where not many women are seen in governance. Besides over 80 per cent of the members of the US House of Representatives, over 75 per cent of the state legislators and 88 per cent of the governors are men.