Once he graced the pages of China's Esquire magazine, but lawyer Xu Zhiyong endured long harassment for his legal activism before he was sentenced to four years in prison on Sunday.

"The power to govern should not come from the barrel of a gun but through votes," believes Xu, whose advocacy for reform ultimately crossed the limits set by the ruling Communist Party.

Born in northern China's Henan province, Xu, 40, studied law at the elite Peking University and become one of an emerging group of "rights defence" lawyers, pushing for political change through court cases.

With a clean-cut, handsome appearance, he came to nationwide prominence in 2003, campaigning against a form of extra-legal detention allowing police to detain people arbitrarily if they travelled away from their rural hometowns. The law was ultimately changed.

The same year he took the defiant step of standing as a non-Communist candidate for a Beijing district People's Congress, a rubber-stamp local legislature.

Xu provided legal aid to several defendants deemed sensitive by the ruling party including blind human rights lawyer Chen Guangcheng -- who later made a spectacular escape from house arrest -- and families who sued after their children were poisoned by toxic milk powder in 2008. Chinese Esquire profiled Xu the following year.

He was seen as a moderate figure seeking to work within the system when calling for change, and fell out with more radical figures such as artist Ai Weiwei, who openly demanded an end to China's one-party state.

"Some even suspected that he had relations with the government," dissident Hu Jia told AFP.

But Chinese authorities do not permit independent and organised forms of dissent, and Xu was arrested in 2009 on tax evasion charges.

They were later dropped but Xu -- whose wife gave birth to a daughter this month -- lived a Kafkaesque existence under surveillance, repeated periods of house arrest, and detentions by state security agents.

Three of them even attended his marriage in 2011, using "video cameras to record the wedding and the guests", Xu's longstanding friend and fellow lawyer Teng Biao told AFP.

The surveillance intensified, friends said, after Xu called for the founding of a "new citizens movement", in which ordinary people would assert their constitutionally-guaranteed rights.

Several hundred followers met for dinners in cities across China, but authorities clamped down after members organised small-scale street protests calling for government officials to disclose their assets, seen as a measure to combat endemic corruption.

Xu was arrested in July on charges connected to small demonstrations in Beijing, including one for access to education.

"Several persons displayed banners, disseminated leaflets, and stirred up rumours in public venues," drawing "a large crowd of onlookers", Xu's indictment says.

His aim was "to get the state to respect the constitution and constitutional safeguards, on a case by case basis", said Eva Pils, an associate professor at the Chinese University of Hong Kong who has studied the New Citizens Movement.

"What from the government's perspective is provocation was the ability to co-ordinate activists and to get people out onto the street."

An account of Xu's interrogation by state security says he was offered leniency if he declared publicly that he supported the Communist Party and vowed to cease his activism.

But Xu "believed he was doing what he had to do, and had not broken any laws. He never thought of yielding to the party or the state security's requests", said his friend Teng.

The Communist Party regularly promises to promote the rule of law but maintains tight control over the courts, and the defence was not allowed to call witnesses at his six-hour trial.

Xu and his lawyers mounted a silent protest during the proceedings, but before the hearing ended, Xu -- who says he has Christian inclinations -- read from a prepared statement until he was interrupted by a judge.

"Common to all those who identify themselves as citizens are the shared notions of constitutional democracy, of freedom, of equality and justice, of love, and faith," the statement said.

"I now finally accept judgment and purgatory as my fate, because for freedom, justice, and love, the happiness of people everywhere, for the glory of the Lord, all this pain, I am willing."