Minnaja graduated with a bachelors in mathematics from the University of Pisa in 1963. He earned his doctorate in Mathematics at the Scuola Normale Superiore di Pisa, and began his academic career as a professor at the Accademia Navale di Livorno in 1965.
In 1973, Minnaja became a mathematics professor in the University of Padua's Engineering Department. He teaches the courses "Mathematics for Electrical Engineering," "History of Mathematics," and "Linear Algebra and Geometry for Information Engineering."
Between 1979 and 1994, he was a member of the Scientific Council of Institute of Computational Linguistics of Pisa. In 1983 and 1984, he was a Visiting Professor at Virginia Tech and UCLA.
Minnaja is a member of the International Academy of Sciences San Marino and a former vice president. He has also lectured in several European universities, and was author or coauthor of fifty scientific papers. Many of which are his books and articles on the international language Esperanto.
In 1980, he received the Culture Award from the Prime Minister of Italy.
In 1960, Minnaja became a member of the Board of the World Esperanto Youth Organization, addressing specialized sections and services. He is still very active in the fields of esperantology and Esperanto literature, and is a member of the literary circle Patrol.
In 1981, he translated Carlo Goldoni's The Mistress of the Inn into Esperanto, and in 1982, he published his translations of the poems of Cesare Pavese.
In 1996, he published his Italian-Esperanto dictionary, which, at more than 1400 pages, is the most comprehensive Italian-Esperanto dictionary.
Minnaja is a member of the Scientific Committee of the Centro Italiano di Interlinguistica, works regularly as a reviewer for the esperanto literary magazine Monato and was editor-in-chief of the magazine Literatura Foiro in 2014.