Former US President Bill Clinton speaks during the second night at the Democratic National Convention in Philadelphia, Pennsylvania, US July 26, 2016. [Photo/Agencies]

After a tough battle with US Senator Bernie Sanders during the state-by-state nominating contests, Clinton is now the party's standard-bearer against Republican nominee Donald Trump.

President from 1993 to 2001, Bill Clinton, 69, left office with high approval ratings and is known as one of the most powerful political orators in the country.

His speech offered an unusual twist to the warm spousal endorsement of a presidential candidate traditionally given in party conventions by a wife, not a man - let alone a former president of the United States.

Hillary Clinton's nomination was a milestone in America's 240-year-old history. US women got the right to vote in 1920 after ratification of the 19th Amendment to the Constitution.