Polce Genakalong, 31, pleaded guilty in the Adelaide District Court to people smuggling.
He was arrested last July on a crowded and poorly-maintained 15-metre wooden fishing boat after a 12-day voyage into Australian waters.
The court was told three juveniles also were arrested.
The Indonesian man's lawyer said his client had been promised $500 to help crew the boat and only realised he was helping smugglers after he was flown to East Java from his home in Timor.
The court was told Genakalong regretted his offending and would never have taken the job if he realised what it involved.
The hearing was told the man had been assaulted in custody by other inmates because of language and cultural issues.
He is to be sentenced next week.