In NT, for instance, a prisoner sentenced to life imprisonment can apply for parole after 20 years. In other States or Territories, the average minimum non-parole period is 10-25 years. This means, a prisoner sentenced to life imprisonment cannot apply for parole until that statutory period is up. However, even if the statutory period is up, there is no guarantee parole will be considered and/or granted.
In NSW, there is no parole period and so prisoners stay in prison for the rest of their natural life. This is also the case at common law.