In 1727-28 Vérendrye was a prominent figure in the extension of New France on its far frontiers and in the search for an overland Northwest Passage to the Western Sea, serving as commander of the trading posts on Lake Nipigon. In 1729 he returned to Quebec and sought to secure official permission and aid in an expedition to search for the Western Sea. Obtaining a monopoly of the fur trade in the West, but no financial support, he entered into partnership with some Montreal merchants and set out in 1731 with three of his sons, Jean Baptiste, Pierre, and François, and a nephew, La Jeremaye. The party founded a number of posts—one on Rainy Lake; Fort St. Charles on the Lake of the Woods; and Fort Maurepas, which was at first on Red River and later on Lake Winnipeg. He returned to Quebec in 1734 but went back to the West with still another son, Louis Joseph.
In the years that followed the Vérendryes continued to explore in the hope of reaching the Western Sea. The eldest of the sons, Jean Baptiste, was killed (1736) by the Sioux. In 1738, Vérendrye made his memorable journey from the Assiniboine River to the Missouri River, where he visited the Mandans. He then returned to Fort La Reine on the Assiniboine, and it is said that he discovered Lake Manitoba in 1739. The most-discussed voyage undertaken by the Vérendryes was that of 1742-43, which was accomplished by two of the sons, probably Louis Joseph (who is generally agreed to have been the son known as the Chevalier) and François. They made a fairly long journey westward, but because of the difficulty of identifying places and Native American tribes, there is no certainty at all as to their route. The earlier hypotheses were shaken when in 1913 some school children discovered near Pierre, S.Dak., the lead plate that had been buried by the explorers when they reached the Missouri on their return. Chiefly because of this discovery, it is now generally thought that the journey did not extend farther west than the Black Hills. The elder Vérendrye sent out next an expedition that went to the Saskatchewan River and also founded two forts, Dauphin and Bourbon, on Lake Winnipegosis, probably in 1741. How far the explorers in this region went it is impossible to say; they may have entered present-day Wyoming.
In 1744, Vérendrye was retired and replaced as commander in the West. In 1749 he was again appointed to that post and was given the Cross of St. Louis. He died before he could accomplish anything further in exploration. His sons wished to continue the work but received no government aid.
The Journals and Letters of Pierre Gaultier de Varennes de la Vérendrye and His Sons were edited by L. J. Burpee for the Champlain Society (1927). See also Burpee, Pathfinders of the Great Plains (1914); biography by N. M. Crouse (1972).