Ma Chun-man is the second person to be convicted under the controversial law that was introduced in Hong Kong last year.
A Hong Kong pro-democracy activist known as "Captain America" has been jailed on secession charges.
Ma Chun-man was found guilty last month of holding up placards and chanting protest slogans for Hong Kong's independence.
He was sentenced to five years and nine months in prison by a court on Thursday.
The 31-year-old former food delivery driver is the second person to be convicted under Hong Kong's National Security Law.
But he was the first to be found guilty of non-violent crimes under the controversial law, which was introduced last year after widespread demonstrations.
Chun-man was known to many people as "Captain America 2.0" because he carried the superhero's shield during pro-democracy protests.
Prosecutors say he chanted words such as "Free Hong Kong, the revolution of our time" and "Hong Kong independence is the only way out".
He had denied the charges and his lawyers had argued that the slogans were "empty words".
Stanley Chan, a specially appointed magistrate, said on Thursday that Chun-man had "the intent and behaviour (of someone) inciting others to secede".
"Whether he used violence, whether he defied law enforcement, whether his ideas were recognised by others - none of that matters," Chan said.
In a handwritten letter to the court, Chun-man said he had "no shame or regrets about what I did".
Amnesty International has described his conviction for secession as "outrageous" and has condemned the Hong Kong government.
Beijing imposed the national security law on Hong Kong in June 2020 and says the legislation has brought stability to the semi-autonomous territory.
But pro-democracy activists say that the legislation has cracked down on all forms of dissent in Hong Kong and more than 100 people have been charged under the law.
The first person to be convicted in July, Tong Ying-kit, was sentenced for riding a motorcycle into police while waving a flag with a protest slogan.
He was imprisoned for nine years on charges of inciting secession and terrorism.
Ma Chun-man was found guilty last month of holding up placards and chanting protest slogans for Hong Kong's independence.
He was sentenced to five years and nine months in prison by a court on Thursday.
The 31-year-old former food delivery driver is the second person to be convicted under Hong Kong's National Security Law.
But he was the first to be found guilty of non-violent crimes under the controversial law, which was introduced last year after widespread demonstrations.
Chun-man was known to many people as "Captain America 2.0" because he carried the superhero's shield during pro-democracy protests.
Prosecutors say he chanted words such as "Free Hong Kong, the revolution of our time" and "Hong Kong independence is the only way out".
He had denied the charges and his lawyers had argued that the slogans were "empty words".
Stanley Chan, a specially appointed magistrate, said on Thursday that Chun-man had "the intent and behaviour (of someone) inciting others to secede".
"Whether he used violence, whether he defied law enforcement, whether his ideas were recognised by others - none of that matters," Chan said.
In a handwritten letter to the court, Chun-man said he had "no shame or regrets about what I did".
Amnesty International has described his conviction for secession as "outrageous" and has condemned the Hong Kong government.
Beijing imposed the national security law on Hong Kong in June 2020 and says the legislation has brought stability to the semi-autonomous territory.
But pro-democracy activists say that the legislation has cracked down on all forms of dissent in Hong Kong and more than 100 people have been charged under the law.
The first person to be convicted in July, Tong Ying-kit, was sentenced for riding a motorcycle into police while waving a flag with a protest slogan.
He was imprisoned for nine years on charges of inciting secession and terrorism.