Sekou Jamal Pendessa, secretary general of the Union of Press Professionals of Guinea (SPPG), was freed after an appeal hearing in the capital Conakry.
Already detained for more than a month, he had been sentenced on Friday to six months in prison, of which three were suspended.
The appeal case saw that reduced to one month in prison, allowing him to walk free.
His release was one of the strikers' main demands.
"It's a victory for democracy, of justice against injustice, of justice against the arbitary," Pendessa said after the ruling.
"The battle against dictatorship continues and we will fight more so that the authorities know they don't have the right of life and death over the population," he added.
After leaving the courthouse, Pendessa met up with fellow unionists to discuss the open-ended general strike in the military junta-led country.
The action was called by 13 unions and is supported by the main political parties and civil society organisations.
In a climate of growing social tension, protesters are also demanding lower food prices, an end to media censorship and improved living conditions for civil servants.
Protests became rare under junta leader General Mamady Doumbouya, who took power in a September 2021 coup, and were banned in 2022.
The strike paralyzed Conakry and was widely followed earlier in the week, continuing to slow down activity across the country on Wednesday. The capital was busier however than in previous days.
Schools, banks, insurance companies and some businesses remained closed.
Administrative offices and hospitals are running skeletal operations.
On Tuesday, the junta said it had appointed a new prime minister, eight days after dissolving the previous government in a surprise move.
The military has arrested several opposition leaders, civil society members and press representatives, while television channels have been removed and radio frequencies disrupted.
Authorities on Friday lifted restrictions on internet access, three months after they were imposed.
Under international pressure, the junta promised to hand the reins of government back to elected civilians by the end of 2024, but the opposition has accused it of authoritarian drift.
Guinea Press Union Head Released From Detention
FILE— Guinea's journalists union leader Sekou Jamal Pendessa celebrates after he was released at the Court of Appeal in Conakry.
CONAKRY, Guinea —A prominent media activist in Guinea, detained for calling a demonstration against censorship, was freed Wednesday on the third day of a general strike, an AFP journalist saw.