Social worker and human rights activist Jolovan Wham wrote a Facebook post in April saying that judges in neighbouring Malaysia were more independent than their counterparts in Singapore on cases with political implications.
He had made the observation as he commented on a legal challenge filed by a Malaysian online news portal against that country's law against fake news.
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Singapore's Attorney-General's Chambers (AGC) initiated contempt of court proceedings against Wham for scandalising the judiciary.
John Tan, a politician with the opposition Singapore Democratic Party, was also charged with contempt after he wrote a Facebook post saying that the AGC's actions against Wham proved that his comments were true.
Wham and Tan argued that their comments constituted fair criticism and were covered under the constitutional provisions for free speech and expression.
High Court Judge Woo Bih Lih however disagreed and convicted the pair.
"Wham's post impugned the integrity and impartiality of Singapore's judges, and thus the Singapore courts," Woo said, adding it meant that local judges "are not completely independent and are partial to the government".
The post also "posed risk that public confidence in the administration of justice would be undermined," the judge said.
Woo said allegations in Tan's post "were not supported by argument and evidence" and "not made in good faith and did not constitute fair criticism of a court".
Sentencing will be passed on another date.
While Singapore is admired for its economic prosperity, it is regularly criticised by rights groups for tough rules on political dissent and freedom of expression.
Last year, the AGC began contempt proceedings against Li Shengwu, a grandson of modern Singapore's founding father Lee Kuan Yew and a nephew of the current prime minister for a Facebook post in which he said the government was "very litigious and has a pliant court system".
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The AGC had described his post as "an egregious and baseless attack on the Singapore Judiciary and constitutes an offence of contempt of court".
Anyone found guilty of contempt could be fined up to Sg$100,000 ($72,141) or jailed for up to three years, or both.
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