Mr Francis Seow, a former solicitor-general who became an opposition politician and then a fugitive from justice, has died in Boston at the age of 88.
His nephew Mark Looi, who lives in the United States, said in a LinkedIn post on Thursday that his uncle had died this week but did not cite the cause.
But Singapore Democratic Party chief Chee Soon Juan said earlier that Mr Seow died of pneumonia.
Mr Seow had been living in the US since 1988 after fleeing Singapore. This was after he was accused of tax evasion and summoned to appear in court.
In May 1988, Mr Seow, who was also a former Law Society president, was detained without trial under the Internal Security Act (ISA) for 72 days in connection with a case involving US diplomat Hank Hendrickson.
The envoy was accused of interference in Singapore politics. He cultivated and advised Mr Seow to set up a more effective opposition in Parliament and to lead a team of lawyers to contest in the general election.
In a sworn affidavit, Mr Seow admitted that he had been to Washington to meet Mr Hendrickson's superior in the State Department. They had assured him of refuge in the US should he run into problems with the Singapore Government.
Shortly after Mr Seow's release from detention in 1988, he contested the September general election in Eunos GRC as a Workers' Party candidate. His three-man team lost to the People's Action Party but secured 49.11 per cent of valid votes.
He fled soon after. Despite claiming he would return to face the tax evasion charges, he never did, and was convicted in absentia in 1991.
He lived in Boston with his daughter Ingrid Annalisa Seow and obtained US citizenship.
Mr Seow began his legal career in Singapore in 1956 when the island was a British colony.
As crown counsel, he led a Commission of Inquiry into a Secondary 4 examination boycott by Chinese students in 1963, at a time when communism was rife.
He also represented the State in the case against two Indonesian saboteurs for the 1965 bombing of MacDonald House which killed three people and injured 33. The duo were convicted of murder and hanged.
Mr Seow rose up the ranks to become solicitor-general - the second-highest rank in the Attorney-General's Chambers. He held the post from 1969 till he resigned in 1972 to enter private practice.
That same year, he was awarded the Public Administration (Gold) Medal for his contributions to the public sector. He became a member of the Law Society in 1976 and was elected its president 10 years later.
As Law Society president, he criticised amendments to the Newspaper and Printing Presses Act that gave the Government powers to curb the circulation of foreign publications deemed to be interfering in Singapore's domestic politics.
Then Deputy Prime Minister Goh Chok Tong accused him of using the Law Society as a political vehicle.
The Legal Profession Act was later tightened to restrict the Law Society's role so it could only "assist the Government in all matters affecting legislation submitted to it". This effectively prevented it from commenting on legislation unless its advice was sought.
In 1987, Mr Seow represented 22 people detained under the ISA for being part of a Marxist conspiracy. A year later, he himself was detained under the ISA.
During his time in exile, he spoke at events at US universities and discussed Singapore politics and wrote several books critical of the Government and judiciary here.
Dr Chee, who posted about Mr Seow's death on his Facebook account, told The Straits Times that he kept in touch with Mr Seow through e-mail until a few years ago.
Mr Seow is survived by his daughter and sons Ashleigh and Andre Seow. They did not respond to telephone and e-mail messages from The Straits Times by press time.