Tony Abbott now officially Australia's 28th Prime Minister

TONY Abbott officially took on the "great responsibility" of Australia's top job on Wednesday, after being sworn in as the nation's 28th Prime Minister at Government House.

In a quiet room surrounded by his family, Mr Abbott took the oath of affirmation with Governor-General Quentin Bryce.

In his first official speech as PM, Mr Abbott told his new Cabinet and outer ministry they would "govern for all Australians", including those who didn't vote for him.

The new government team will include 18 cabinet ministers, including the first female Foreign Minister, Julie Bishop, 11 assistant ministers and 12 parliamentary secretaries.

Keen to create an impression of getting down to work, Mr Abbott said the new government hoped to be "judged by what we have done, rather than by what we have said we would do".

"We aim to be a calm, measured, steady and purposeful government that says what it means and does what it says," he said.

"We won't forget those who are often marginalised, people with disabilities, indigenous people and women struggling to combine career and family."

After the ceremonies, the new Coalition Government passed on the traditional Cabinet photograph, instead opting to have a single picture taken of the full ministry.