"It's a very heavy verdict for Khaled Drareni. We are surprised, the case is hollow," lawyer and President of the Algerian League for Human Rights Nouredine Benissad told AFP.
Drareni, 40, editor of the Casbah Tribune news site and correspondent for French-language channel TV5 Monde, was arrested on March 29 on charges of "inciting an unarmed gathering" and "endangering national unity" after covering demonstrations by the "Hirak" protest movement.
The Hirak protests last year swept ailing president Abdelaziz Bouteflika from power but continued afterwards, demanding the ouster of the entire state apparatus, reviled by many Algerians as inept and corrupt.
Weekly protests rocked Algeria for more than a year and only came to a halt in March due to the novel coronavirus crisis.
Two co-accused in the trial, Hirak protesters Samir Benlarbi and Slimane Hamitouche, were sentenced to two years' jail each, said Benissad, a lawyer with the defence team which plans to appeal the sentences.
Press freedom watchdog Reporters Without Borders (RSF), for which Drareni also works, condemned the sentence against him as "arbitrary, absurd and violent".
"This is clearly a judicial persecution against a journalist who is the honour of his country," said RSF Secretary General Christophe Deloire.
"Justice under orders has just made Khaled Drareni a symbol that will arouse global indignation and mobilisation."
The prosecutor had called for Drareni to be sentenced to four years in prison, fined and stripped of his civil rights at the opening of his trial at the Sidi M'hamed court in Algiers on August 3.
A gaunt-looking Drareni denied the charges when he appeared via video conference due to coronavirus measures.
"I just did my job as an independent journalist," he said, according to an RSF statement, arguing he had exercised his "right to inform as a journalist and citizen".
RSF, part of an international support committee for Drareni, had earlier said that "a prison sentence would be proof of a shift to authoritarianism" in the north African country.
If judges were to "accept this absurd indictment, it would show that Algeria's judiciary and executive have turned their back on the ideals of the country's independence," Deloire said before the sentencing.
The US-based Committee for the Protection of Journalists had also demanded Algeria "immediately and unconditionally release journalist Khaled Drareni, especially as there is no evidence he did anything except his job as a journalist".
The Algerian judiciary has stepped up prosecutions and convictions of journalists, Hirak activists, political opponents and bloggers in recent months.
Some journalists have been accused of sowing discord, threatening national interests and being on the payroll of "foreign parties", with several in prison and trials under way.
In July, Ali Djamel Toubal, a correspondent for the privately-owned media group Ennahar, was sentenced to 15 months in prison for, among other things, broadcasting footage showing police officers mistreating anti-regime demonstrators.