He took out the non-fiction section, earning $25,000, before going on to win the $100,000 Victorian Prize for Literature, the most valuable literary award in the country.
While conditions stipulate that authors must be Australian citizens or permanent residents of Australia, organisers The Wheeler Centre made an exception for Mr Boochani.
"In some ways, I am very happy because we are able to get attention to this plight and you know many people have become aware of this situation, which is great ... But on the other side I feel that I don't have the right to have celebration - because I have many friends here who are suffering in this place," Mr Boochani told the BBC.
"[The] first thing for us is to get freedom and get off from this island and start a new life."
Mr Boochani has been ineligible to enter other Australian literary awards including the Walkley book award and the NSW Premier's Literary Prize as he is not an Australian citizen.
The Kurdish journalist has been on Manus Island since 2013 after fleeing Iran and the book is a record of his time there.
"Laboriously tapped out on a mobile phone and translated from Farsi, it is a voice of witness, an act of survival, a first-hand account, a cry of resistance, a vivid portrait through five years of incarceration and exile," shortlist material from The Wheeler Centre says.
The regional processing centre on Manus Island's Lombrum Naval Base closed in 2017 but there are about 600 refugees living in camps in the main town of Lorengau.
A recent report by Amnesty International claimed that since August 2017, three men have killed themselves while many others have attempted suicide.
The offshore policy is designed to deter people embarking on treacherous sea journeys, but the United Nations and other rights groups have criticised the camps' conditions and the long detention periods.
Readers seeking support and information about suicide prevention can contact Lifeline on 13 11 14, Suicide Call Back Service on 1300 659 467 and Kids Helpline on 1800 55 1800 (up to age 25). More information about mental health is available at Beyond Blue.