He was the first person to stand trial and be convicted under a colonial-era sedition law since the 1997 handover.
Tam was earlier found guilty of chanting seditious slogans such as ‘Liberate Hong Kong’ on several occasions from January to July 2020.
The 50-year-old activist was also convicted of four counts of public order offences, including holding an unauthorised assembly and disorderly conduct in a public place.
His lawyers had pleaded for a lenient sentence, saying Tam has never advocated violence and was only using “extreme remarks” to express his emotions.
But District Court Judge Stanley Chan said a deterrent sentence was needed, because some of the offences were committed after the national security law came into force, and while Tam was out on bail.
The judge – appointed by the Chief Executive to handle national security cases – also stressed that the court has to consider the social and political reality at the time, noting that the offences happened just after “unprecedented violence” in 2019.
The judge described remarks made by the activist as merely “boundless abuses from a 50-year-old uneducated man”.
Tam was also fined HK$5,000 for one of the offences.
The activist has been detained since September 2020.