Ylieff was born in Verviers, Liège, to a Bulgarian emigrant family. He graduated in history before engaging in politics. In 1973, he was elected mayor of the municipality of Dison, a position he held until 2018. From 1974 to 1995, he was a member of Belgian Chamber of Representatives, the lower house of the Belgian Federal Parliament. In 1988–1989, he was a Minister of National Education of Belgium; from 1989 to 1992, he served as the French Community of Belgium's Minister of Culture and Higher Education.[1] In 1995–1999, he was federal Minister of Scientific Policy[2][3] and from 1999 to 2003 he was Government Commissioner of Scientific Issues.