In order to gain Australian citizenship, you have to demonstrate that you are of good character.
You must inform the Department of Immigration and Border Protection if you have been convicted and received a fine, a good behaviour bond, suspended sentence or a period of imprisonment. In saying this minor speeding fines and parking fines are not included.
A person would usually find it hard to obtain citizenship if they have committed a serious offence.
The only time you would not have to disclose a conviction is if you have not been convicted of a minor offence for the 10 years prior to applying for citizenship.