Clinton declared herself the Democratic Party nominee on Tuesday evening after winning the New Jersey primary, setting up a general election campaign against Republican candidate Donald Trump in the Nov 8 election.
She is the first woman in American history to attain the presidential nomination of a major political party.
Hailing a milestone, Clinton declares victory in Democratic race
"As a father of two daughters, I'm proud," Kerry told reporters while traveling from China to the United Arab Emirates, adding he had sent a message to Clinton congratulating her on the outcome.
"She'll make a terrific president." Kerry, who was the Democratic nominee for president in 2004 but lost to Republican incumbent President George W. Bush, said Clinton's achievement was a "truly historic moment for the nation."
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"Everybody ought to celebrate it, Republican or Democrat alike," he said.
"It's a breakthrough, and I think that whether you're voting for Trump or you're voting for her or whoever, you ought to take pride."
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