Gilles Joseph Gustave Dewalque was born on December 2, 1826, in Stavelot, Belgium.

He was a Belgian geologist, mineralogist, cartographer, professor, and author. He received his primary and secondary education in Liège. In 1844, he entered the University of Liège, where he received the degree of M.D. in 1853 and D.Sc. in 1854. In 1855, he was offered a position of a professor of mineralogy, geology, and paleontology at the University of Liège. In 1854, he was appointed correspondent of the Royal Academy of Sciences and Belles-Lettres of Brussels and became its member in 1859. In 1873, he became one of the founders of Société géologique de Belgique and Commission de la carte géologique de Belgique. In 1875, he proposed the creation of a large-scale geological map of Belgium which was completed in 1879. The same year he retired and became a Professor Emeritus of the University of Liège. He was also a foreign correspondent of the Accademia Pontificia dei nuovi Lincei, the Academy of Natural Sciences in Philadelphia, the Academy of Valdarno, and the Imperial and Royal Geological Institute of Austria. He was an honorary member of the Imperial Mineralogical Society of St. Petersburg and a foreign member of the Geological Society of London. He published more than 550 works in the field of his study. He was a recipient of the Order of Leopold (Ordre de Léopold), the most important military and civil order in Belgium.

In 1876, he married Céline Lambotte (1842–1915). He died on November 3, 1905, in Liège, Belgium.