During a speech to the National Press Club at lunchtime, Ms Gillard took the unusual move of announcing the election several months out from polling day.
She says the decision was based on summer deliberations and on the grounds of certainty.
“Time is not for wasting, so decisions have to be made about how we use our time this year,” she says.
Ms Gillard added that Independent MPs Tony Windsor and Rob Oakeshott were told by phone before the rest of the Labor Party.
The writs for the election will be issued on August 12, setting up a short parliamentary year until the election.