Peter Symon’s London-born father, Eric, was a devout Christian when he enlisted during World War I, but he returned home with gas-damaged lungs and a firm commitment to communism. Eric then emigrated to Australia as a soldier settler to South Australia. His wife Rosina May (nee Symons), arrived later with their son David. Peter Dudley was born shortly afterwards, and a sister, Helen, some years later.
During the Depression the family was forced to leave the farm after a prolonged drought, and Eric, an original member of the Communist Party of Australia's South Australian branch, established the Anvil Bookshop in Adelaide.
Peter attended Unley High School, but to support the family he quit at 14 to work in a haberdashery store. He saw mass unemployment and evictions, and during the Spanish Civil War he became convinced that capitalism should be abolished, so at 16 he joined the Communist Party.
In 1941 he enlisted, and became an army education officer. He served in Darwin during the air raids, but in 1943 transferred to the RAAF and trained as a navigator-wireless operator, flying on aircraft "ferry" flights between Victoria and New Guinea. Although on one early flight his aircraft was forced to land off course and out of fuel on a Queensland beach, the RAAF promoted him to a flying officer navigator, and at the end of the war offered him a commission.
Symon chose a different course. His father had died, so he took over the bookshop, and went back to party organisation work. In 1950, during the Menzies government's attempts to ban the Communist Party, their home was raided twice. Several publications were seized - including a knitting book. Brandishing an iron, May Symon guarded the door to the room where Helen lay bedridden with polio, from which she later died.
Symon married Phyllis Osmond that year. He was entitled to the former-servicemen's tertiary education grant, and wanted to study at university. However, he had not matriculated, and in 1951 went to work on the Adelaide wharves, later becoming secretary of the party's South Australian waterside workers' branch.
The party lost many members because of the Cold War and because of deep divisions within the party over the Soviet interventions in Hungary in 1956 and Czechoslovakia in 1968. Symon, however, saw both interventions as necessary to defend socialism against counter-revolution.
In the mid-1960s a group within the party leadership started full-scale denunciation of the Soviet Union, abandoning concepts such as the class struggle. Symon disagreed, arguing that blanket denunciation was just as simplistic as the view that the Soviet Union could do no wrong. He believed the Australian party should analyse recent history, ensure that mistakes made by communists within Australia and elsewhere were not repeated, and recognise the achievements of the world's communist parties and governments.
Symon wanted to study economics, and matriculated in 1968. However, in 1970, after unsuccessful attempts to change the party leadership, some CPA members formed a new party, the Socialist Party of Australia (SPA). Based on the works of Marx, Engels and Lenin, it was intended to maintain the best practices of the old party and a commitment to the working class.
In 1971, Symon was elected as SPA general secretary, and moved to Sydney. So began 37 years in which he led his party in campaigns against exploitation, war, the nuclear threat, the arms race, discrimination, environmental degradation and the threat of climate change. He opposed Gorbachev's ideological line in the 1980s, and was appalled by the collapse of the Soviet Union, but he saw it as a setback in the long historical path to socialism, not a defeat.
In 1991 the Communist Party was dissolved. Five years later the Socialist Party, which had maintained the old party's original ideology, reclaimed its title and became the new Communist Party of Australia.
Symon drew encouragement from the development of China and the other socialist countries, and by the emergence of new forces, including the left-wing and socialist governments in South America. He believed that the Greens and progressive independent parliamentarians were an alternative.
He could give a rip-roaring speech, but he felt that communists should use tactics most effective to the circumstances. He won the respect of his international peers and many political adversaries. He vigorously opposed the death penalty. He believed that only socialism could deal adequately with climate change, and that without it the oil and coal corporations would block effective and timely remedial action.
The Symons were divorced in 1973, but remained good friends. Symon married Natasha (nee Starovoitova) in 1977. They lived frugally in a tiny terrace crammed with books, notes, pictures and recordings. He had a good sense of humour, but some people found his habitually serious demeanour intimidating. His Depression-era youth left him with sometimes maddening habits of thrift, and many people marvelled that he survived to 86, given his unnerving late-in-life habit of accelerating towards red traffic lights.
Neither dogmatic nor opportunistic, he never compromised his ideological integrity, and his loyalty to Australia's working people was unwavering.
Peter Symon is survived by Natasha, brother David, former wife Phyllis Schneider, son Brian, daughter Jenny Elwin, and six grandchildren.