A first-generation Singaporean born to a court interpreter father and a Hainanese mother who worked as a washerwoman, Ngiam won a bursary to study economics at the University of Malaya. Later in his career he obtained a Masters in Public Administration at Harvard University.

In 1970 – five years after Singapore gained full independence – Ngiam became the nascent republic’s youngest ever permanent secretary, in the Ministry of Communications, at age 33.

Following a stint as chairman of the Economic Development Board, he took on senior positions in the finance, trade and industry, and national development ministries.

From 1979 to 1994 he concurrently served in the Prime Minister’s Office, where he worked under Lee Kuan Yew and his successor Goh Chok Tong.

Han Fook Kwang, the former chief editor of The Straits Times, first encountered Ngiam four decades ago when he was starting out as a young civil servant in the Economic Development Board. Ngiam was then the chairman of the agency.

“My generation of public service officers looked up to him and the pioneer generation of civil servants not just because of their public policy abilities but more because we were able to see first hand what drove them to serve and the values they lived by,” Han said. “His work was his life and he was completely devoted to it.”

Han said Ngiam continued to be concerned about Singapore even after his retirement in 1999.

To younger Singaporeans, Ngiam is best known for his post-retirement criticism of the PAP and the Administrative Service, the bureaucracy’s top echelon that the ruling party regularly taps for fresh blood.

He was among a handful of establishment insiders who publicly aired their grievances about the system, and yet were left relatively unscathed by the PAP – known otherwise for its hold-no-prisoners approach to high-profile dissenters.

In a 2003 interview, he told The Straits Times the bureaucracy’s biggest danger was that “we are flying on autopilot”.

Pressed on why this had come to be, Ngiam said: “There is also a particular brand of Singapore elite arrogance creeping in. Some civil servants behave like they have a mandate from the emperor. We think we are little Lee Kuan Yews.”

In the same interview, he urged the country’s leaders to accept that the city state was larger than the PAP, and urged it to end the practice of placing all government scholars in the civil service as a way of preserving its own longevity.

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“It is the law of nature that all things must atrophy. Unless [Lee Kuan Yew] allows serious political challenges to emerge from the alternative elite out there, the incumbent elite will just coast along,” Ngiam said.

More controversial was a 2013 interview with the official publication of the Singapore Medical Association.

This time, Ngiam challenged the PAP’s long held argument that political office holders need to be highly paid not only to deter corruption, but to ensure top talent in the private sector can be persuaded to enter public service.

“When the salary is so high, which minister dares to leave, unless they decide to become the opposition party? As a result, the entire political arena has become a civil service, and I don’t see anyone speaking up any more.”

The remarks sparked sharp consternation within the ruling elite, and Ngiam subsequently walked back his comments, saying they were “illogical” and that he had been unaware that some ministers came from humble backgrounds.

Prime Minister Lee chimed in after the U-turn, saying in a tersely worded statement that he hoped that Ngiam in retirement would “continue to support the institutions and systems that he helped build during his long and illustrious career.”

There was no immediate comment from the prime minister following the news of Ngiam’s death. Goh, the country’s prime minister from 1990 to 2004, said he worked under Ngiam as a young civil servant and “learnt much from him”.

Noting that the top bureaucrat earned a reputation as Singapore’s “economic czar”, Goh said Ngiam served the country “with distinction”.

Han, the civil servant-turned-newspaper editor, said that on retirement – with the lifting of constraints on speaking publicly about the government – Ngiam spoke his mind on “matters he believed were important”.

“When you are outside of the system, your perspective can change and you see some issues in a different light compared to when you are inside,” Han said.

“The difference was that Mr Ngiam spoke up when others might have preferred to keep quiet. But whether inside or outside he was driven by the same values which shaped his civil service career.”

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Inderjit Singh, a former member of parliament, said many of Singapore’s strong government institutions came about because of people like Ngiam.

“That generation [of public servants] were willing to challenge the political leaders when needed and there was healthy debate which is why Singapore became successful,” he said.

After retirement, Ngiam saw a different approach taken by the civil service and government and he spoke up unlike many retired civil servants who chose not to comment about successive leaders, Singh said.

“We can call him a loving critic. His intentions were for the betterment of Singapore and he spoke up because he felt things were going in a direction that may not be good for Singapore’s future.”

Political analyst Loke Hoe Yeong, who edited the book Speaking Truth to Power that features Singapore's pioneer public servants including Ngiam, said the late bureaucrat was ahead of his time in pushing for Singapore to adopt an export-orientated industrial model rather than import substitution, which was more in vogue in the 1970s.

"History would prove that he was ahead of his time and he made all the right economic decisions," Loke said.

Ngiam is survived by his wife Jeanette Gan Choon Neo, two children and three grandchildren, according to The Straits Times.