As Groulx was looking for a successor, he spares Frégault a training stay in the United States to avoid what he experienced himself, "the chore of improvisation in a profession where one does not improvise." Upon his arrival at Loyola University Chicago, Frégault had no research subject. Father Delanglez, who was to be his advisor, offered him a spot at "The quarry of Pierre Le Moyne d'Iberville". Delanglez would come to strongly influence Frégault. At first, he was a little disconcerted by the learning required as a historian, but he quickly adjusted and completed his studies at a fast pace. In June, 1942, just 18 months after his arrival in Chicago, he began writing his doctoral thesis, entitled "Iberville the Conqueror," which was published in 1944. In the fall of 1943, Frégault inaugurated the first historical methodology course that had ever been offered in a Quebec university and, at the same time, introduced the practice of history seminars while teaching a course on the public institutions of New France. Chartier, who was asked to appoint his successors for the seven positions he held at "Université de Montréal" on June 24, 1944, entrusted Frégault with Canadian literature. At the same time, also thanks to Chartier (who had a long-standing relationship with Grolier), Frégault became one of the principle contributors to the French-Canadian of its encyclopedia, which began to appear in 1947. At the creation of the "Institut d'histoire" (Institute of History), Robert Rumilly took over from Frégault at Grolier. A few months after the publication of "Iberville the Conqueror—"a book through which he would become the first winner of the Duvernay Award of the Saint-Jean-Baptiste Society of Montreal"—"he published "The Civilization of New France". The close publication of the two works earned him a solid reputation as a historian as early as 1944. In 1945, aged 26, Frégault became a founding member of the Académie des lettres du Québec and received the Vermeil Medal from the Société historique de Montréal (Montreal Historical Society). In 1947, he was the first recipient of the "prix David", which he was awarded for "Iberville the Conqueror" and "The Civilization of New France". From September, 1946, to May, 1947, he was the director of "L'Action nationale".