Over more than four decades, Mr. Haigh used his roles — first in diplomacy and later as a columnist — to challenge Australia’s leaders as a self-styled voice of conscience. He was willing to “tilt at any windmill” where he sensed injustice or imbalance, one Australian commentator wrote. Among his prime targets: harsh refugee policies and the strong U.S. sway over Australia’s diplomatic and military decision-making.

“I have this anger about things that are not right,” he once said. There was no surprise that he was never an easy fit in the often-nuanced world of diplomacy after joining Australia’s foreign service in 1972. He found ways, however, to use his envoy status as a powerful tool after he arrived in South Africa in 1976 as second secretary at the embassy in Pretoria.

Mr. Haigh recalled that his glimpse of South Africa’s racial divides came before his plane touched down. Waves of protests had broken out in the Black township of Soweto. “Apartheid,” Mr. Haigh said, recounting his view from the plane, “was laid out below.”

“Cramped, drab and draped in coal smoke, the narrow streets and small box houses of the African townships stood in marked contrast to the pool-studded mansions,” he said.

Mr. Haigh was soon making contacts with Black activists, including Steve Biko. He was not the only diplomat challenging the apartheid system, which had left South Africa largely isolated because of boycotts and sanctions. Mr. Haigh, however, was among the most active diplomats in anti-apartheid outreach and was given unusually wide latitude by his embassy to pursue contacts and intelligence gathering.

South African authorities were always watching. Mr. Haigh was watching, too, and became skilled at evading them.

A remote spot outside the southeastern city of King William’s Town (now called Qonce) was chosen for his first meeting in 1976 with Biko, a leader among a younger generation of activists gaining prominence more than a decade after the jailing of Nelson Mandela. Under police orders, Biko was restricted from leaving King William’s Town. Mr. Haigh had to secretly come to him.

“We sat under a tree and talked for three or four hours,” Mr. Haigh recalled.

Biko gave Mr. Haigh access to the inner leadership of the apartheid fight. Yet within a year, Biko was dead — arrested in August 1977 and killed in custody the next month.

Biko’s funeral became one of the galvanizing events of the anti-apartheid movement and stirred rage over the abuse he endured. Testimony two decades later, during post-apartheid Truth and Reconciliation Commission hearings, said the torture inflicted on Biko included smashing him into a wall headfirst like a “battering ram.” No one has been convicted.

Mr. Haigh said he was at home in Pretoria when he received the call about Biko’s death from Donald Woods, the White editor of a South African newspaper, the Daily Dispatch, who had become impressed by Biko’s indomitable spirit. Woods had gone into the morgue with Biko’s wife and photographed Biko’s battered body. (The images would become part of the reporting for Woods’s 1978 book, “Biko.”)

Because of his ties to Biko, Woods was placed under house arrest. He also feared retaliation from authorities. A T-shirt treated with a chemical substance was mailed to his 6-year-old daughter, presumably by security officials. It left the girl with burns on her face and arms.

Mr. Haigh had arranged to meet Woods in person, because it was too risky to talk by phone. He asked Woods if had thought about fleeing the country.

“And he said, ‘Yes, I have,’” Mr. Haigh told the Sydney Morning Herald in 2013. “And I said, ‘Well, I am happy to take you.’’’

The initial plan was for Mr. Haigh to drive Woods to Botswana, hiding him under blankets in Mr. Haigh’s embassy car. Instead, Woods disguised himself as a priest and crossed on foot into Lesotho on the last day of 1977. Mr. Haigh was waiting on the other side and helped get Woods on a U.N. plane to cross South African airspace en route to Britain. Woods’s family later joined him.

Mr. Haigh said none of his diplomatic colleagues knew about the escape. “I didn’t trust anyone,” Mr. Haigh said. “I was freelancing. I was a people smuggler.”

Details of Mr. Haigh’s role were kept under wraps for years. In the film “Cry Freedom,” based on the interwoven stories of Woods (played by Kevin Kline) and Biko (Denzel Washington), there is a character named Bruce Haigh (John Hargreaves), but he is not a diplomat.

“To protect my identity,” Mr. Haigh said, “I was portrayed as an Australian journalist.”

Bruce Douglas Haigh was born in Sydney on Aug. 6, 1945, and his family eventually settled in Perth.

In 1964, he signed up as a ranch hand, known as a jackeroo, after embellishing his abilities on horseback, and was sent to the Kimberley, a vast region in northwestern Australia. He also worked on an oil rig before serving in the army during the Vietnam War.

He graduated in 1971 from the University of Western Australia, writing his thesis on Australian political cartoonists for his dual history and politics degree. He said the politics department supported the idea; the history faculty was less impressed. “It was my first dust-up with bureaucracy,” he told the Melbourne Age.

He joined Australia’s Department of Foreign Affairs the following year — and complained that the diplomatic training emphasized conformity over bold thinking. “We had not been collected together to learn,” he wrote, “but to be institutionalized.”

He stuck with it and was posted to Islamabad in 1973 as third secretary in the embassy. He became one of the first diplomats to meet Pakistan’s Benazir Bhutto, who was back from studies at Oxford and was being groomed for a place in the family political dynasty. They became friends. After becoming Pakistan’s prime minister in 1988, she contacted Mr. Haigh directly to arrange shipments of Australian wheat.

Mr. Haigh rose higher in the diplomatic corps with postings to Saudi Arabia, Indonesia and then back to Pakistan from 1986 to 1988. He resigned from the diplomatic service in 1995 after a short stint in Sri Lanka.

He was then appointed to Australia’s Refugee Review Tribunal, which held hearings for asylum appeals. Also on the tribunal was Biko’s former defense attorney, Shun Chetty, who said Mr. Haigh spirited him out of South Africa in 1979 in the back of a diplomatic car.

Mr. Haigh left the panel in 2000 and became a leading critic of Australia’s refugee policies, which included sending people to encampments on the Pacific island nation of Nauru and other sites, where they sometimes waited years in limbo.

In a 2016 column, he compared Australia’s restrictive refugee system to the racism of apartheid. “The black shirts of Border Force [have] adopted the same mentality for similar reasons,” he wrote.

Mr. Haigh’s first marriage, to Lysbeth “Libby” Mosley, ended in divorce. Their son Angus died in 2016. Survivors include his second wife, Jodie Burnstein; a son from his first marriage, Robert; two daughters from his second marriage, Samantha and Georgina; and a sister.

In 2006, a collection of 50 apartheid-era artworks and memorabilia was returned to South Africa under the Ifa Lethu Foundation, led by Biko’s eldest son, Nkosinathi. Mr. Haigh and another former Australian diplomat, Di Johnstone, helped create the foundation in the hope that younger generations do not lose touch with the past.

“My commitment in fighting apartheid was strong,” Mr. Haigh said, “but the emotional toll was high.”