"It is a travesty of justice. It is simply wrong. It is going to be historically proven that Indonesia is on the wrong side of history,” Mr Harsano told SBS News.
Protests have been staged across the country this week, showing Indonesians and Melanesian Papuans standing side-by-side in solidarity, calling for the group of men to be released.
The issue has spawned the hashtag #PapuanLivesMatter a reference to the Black Lives Matter protests that have swept the world in response to the killing of black man George Floyd at the hands of police in the United States.
Last August and September, tens of thousands of Papuans took to the streets across Indonesia in protests sparked following a racial slur by Indonesian authorities against Papuan students in Surabaya, East Java, in August.
As the anti-racism movement gained traction, some of the demonstrations evolved to see many calling for West Papuan independence.
Human Rights Watch is urging authorities to drop the charges.
"They did nothing wrong. What they did was a justified, a freedom of expression, raising their concern against racism in Indonesia. They were not involved in violence. They did not instigate violence. One of them even denounced the protests," Mr Harsano said.
Indonesian human rights lawyer Veronica Koman, who is now living in exile in Australia, says the seven men accused of treason are being used as scapegoats.
“They are being scapegoated over this uprising. West Papuans have been saying that Indonesian law is racist towards West Papuan people and I truly agree to that notion,” Ms Koman said.
A military crackdown across West Papua to quell the protests saw tens of thousands of additional Indonesian soldiers and officers deployed in the region.
Dozens of Papuans were arrested and humans rights observers say 46 still remain behind bars.
The seven Papuan men facing sentence on Wednesday have become known as the ‘Balikpapan 7’ because after being arrested in Jayapura, in the province of Papua, they have been detained and will be sentenced in Balikpapan, East Kalimantan (Borneo) which is located thousands of kilometres away from their homes.
Indonesian authorities say the men were taken to Borneo for security reasons.
The defendants include: Buchtar Tabuni, a leader of the pro-Papuan independence group United Liberation Movement for West Papua. Indonesian prosecutors are seeking a 17-year prison term for Mr Tabuni.
Agus Kossay and Stevanus Itlay from activist group the National Committee of West Papua (Komite Nasional Papua Barat) both face potential sentences up to 15 years in jail.
Ferry Gombo, a student at Cenderawasih University and Alexander Gobai a student from Jayapura University of Science and Technology both face up to 10 years behind bars.
While two other students, Irwanus Uropmabin and Hengki Hilapok, face up to five years in prison for allegedly helping Mr Gobai to rent a truck and sound system for the protests.
“This is very appalling and it shows the systemic racism embedded within the law,” Ronny Kareni of activist group, United Liberation Movement of West Papua, said.
An online petition has been set up calling for the men to be released.
Rights groups in Indonesia say there has been escalating intimidation and security threats in the run-up to Wednesday’s verdict in the treason trial.
Papuan demands for independence or greater autonomy is among the most sensitive topics in Indonesia, but campaigners said the latest intimidation reflects a worsening political atmosphere across the archipelago of 270 million people.
"We have recorded at least 20 incidents in which students, academics, journalists, and activists, have been intimidated for criticising the government and discussing politically sensitive issues, such as rights abuses in Papua," Usman Hamid, local executive director of Amnesty International, said.
SBS News has contacted the Indonesian embassy in Canberra but is yet to receive a response.