While public servants must serve in the public interest,it is up to the elected government to decide what the public interest is,Mr Pezzullo said in an address to the Institute of Public Administration Australia on Tuesday.
"It would be mortally dangerous to our system of government for the public service to come to possess an aggrandised conception of its role in the proper processes of government – as the ultimate guardian of'the public interest',located outside of the political process."
"There is no legitimate basis for contending that unelected officials have any purportedly'supranational'responsibility as custodians of the'public interest',somehow separately identified from the domain that is termed too often to be that of'politics'."
Democracy means that only ministers can decide on major issues of policy,even though it is only the public service that can give the best advice to government.
"A public service which does not see itself conjoined to this endeavour has lost its way,"Mr Pezzullo said.
An apolitical public service is one of the key institutions of the Westminster system of government,Mr Pezzullo said,but public servants can't avoid politics.
"There is no inconsistency in the[Australian public service] being both responsive to the government,on the one hand,and simultaneously existing as an apolitical career service to enhance the effectiveness and cohesion of Australia’s democracy."