Originally from Amarah in the southern Maysa governorate, his parents had moved to the capital before his birth and opened a bistro next to the Directorate of General Security, where the young Selim often worked after school.

His autobiography recounts it as a seminal moment: "The poor boy from the south whose dream was limited to being accepted by a family, however small, was suddenly part of this large international family made up of magnificent Europeans, blond, civilized and full of illustrious characters: Lenin, Marx, Engels, Mao, Castro as well as other intellectuals, scientists, politicians and activists.

Kicked out of the camp after a week for criticising the party's bureaucratic structure, he subsequently migrated throughout the Middle East over the following two years, "accumulating experiences that were as revolutionary and impulsive as they were naïve and thoughtless..."[5] He became intensely disillusioned by the Iraqi opposition's factionalism and infighting, which was further worsened by the manipulations of secret service infiltrators and external groups: "They used us as pawns on a chessboard by sheltering behind revolutionary slogans.

"[4][5] Deeming himself unfit for the life of a militant, Matar decided instead to serve the Iraqi cause through cultural avenues and made plans to seek an education in Europe;[4][5] after securing an Italian visa, he moved to Rome in late 1980 and spent the following eight months in abject poverty.

[5] Matar's first attempted move to Switzerland was aborted when his money and documents were stolen; he finally settled in Geneva in late 1981[4][6] and enrolled in the Graduate Institute of International and Development Studies, specializing in Social Sciences and research in the Third World.

Matar's adherence to pacifism, belief in national unity and opposition to ethnic and religious sectarianism has been the source of controversy inside and outside of Iraq.

Khamsat alâf 'âm min al-tadayyun al-'irâqî (2006; English translation: 5000 Years of Iraqi Religiosity) Detailing the history of the different religions and confessions of Iraq.

Mawsû’at al-bî’ah al-'irâqiyyah (2010; English translation: Encyclopedia of the Iraqi Environment) Detailing the geology and nature of Iraq, as well as the ecological challenges caused by industry, conflict, and pollution.