When NSW District Court Judge Reg Blanch imposed the minimum sentence on Mr Magaming in 2011, he said that he was a simple fisherman whose part in the offence was at the bottom of the scale of seriousness, and he would have given him a much lesser sentence if he had any discretion.

In August last year, the Gillard government moved to restore judicial discretion, with then-attorney-general Nicola Roxon issuing a directive to the Commonwealth Director of Public Prosecutions that first-time offenders and ''low culpability crew'' be charged with offences that do not carry mandatory prison terms.

This followed a recommendation from the expert panel on asylum seekers led by former defence chief Angus Houston that discretion be restored to courts in relation to sentencing. But the Coalition has promised to revive mandatory sentences for asylum boat crews.

''There needs to be a strong message that supporting people smugglers by crewing their boats is a crime and that Australia takes these crimes seriously,'' Mr Morrison said in September last year.

Mr Magaming had argued to the High Court that prosecutors had impermissibly exercised judicial power by choosing to charge him with an offence carrying a mandatory minimum sentence when another offence which did not carry a mandatory prison term was available.