The 76-year-old has been in prison for almost four years and faces the possibility of spending the rest of his life there.

He is the first person to contest a charge of "collusion" with foreign powers under Hong Kong's national security law, imposed in 2020 after huge, sometimes violent democracy protests engulfed the city the previous year.

Here is what we know about Lai:

- 'Troublemaker' -

A rags-to-riches millionaire, Lai is a self-styled "troublemaker".

He was born in mainland China's Guangdong province into a wealthy family that lost everything when the communists took power in 1949.

Smuggled into Hong Kong aged 12, Lai toiled in sweatshops, taught himself English and eventually founded the hugely successful Giordano clothing empire.

He established his first publication shortly after the 1989 Tiananmen Square crackdown, writing columns that regularly criticised senior Chinese leaders.

Asked why he did not keep quiet and enjoy his wealth like other Hong Kong tycoons, Lai told AFP before his arrest:

"Maybe I'm a born rebel, maybe I'm someone who needs a lot of meaning to live my life besides money."

His two primary outlets -- Apple Daily newspaper and Next magazine -- were hugely popular in Hong Kong, mixing tabloid sensationalism with hard-hitting political reportage.

They were also among the few publications that openly backed the 2019 protests.

Lai was vilified in China's state media as a "traitor".

- Bail denied -

He was first arrested in August 2020 when Hong Kong police raided Apple Daily and paraded him through the newsroom.

A judge briefly granted him bail in December 2020 on steep conditions, including posting HK$10 million ($1.28 million), but that lasted only a week before the top court ordered him back to prison.

He has been there ever since, with his son Sebastien Lai calling him "the oldest political prisoner in Hong Kong".

A tougher set of bail rules now apply to national security cases since the reversal in Lai's case, affecting dozens of other prosecutions.

Lai, who holds a British passport, was also denied his choice of representation for his collusion trial: veteran British human rights lawyer Tim Owen.

Hong Kong courts initially sided with Lai, but Beijing responded by granting new powers to Hong Kong's leader to screen overseas lawyers in security-related cases.

The city's pro-Beijing legislature went a step further in May 2023, passing laws requiring overseas lawyers to get special permission to join security cases.

- 'A death knell' -

Lai has already been found guilty in five other cases.

He was handed a sentence of 20 months for organising and participating in marches during the democracy protests that formed the basis of four prosecutions.

He was convicted in the fifth case of "conspiracy to defraud" for breaching the terms of an office lease. That added another 69 months to his sentence.

Separately, he tried to stop police from going through two of his cell phones, citing legal protections against searching journalistic materials, and attempted to protect his Apple Daily shareholder voting rights after the company's assets were frozen.

Lai lost both cases after High Court judges stressed the importance of national security.

He told AFP before his arrest in 2020 that Beijing's national security law would be "a death knell for Hong Kong".

"It will supersede or destroy our rule of law and destroy our international financial status," he said.