John Baptiste McLoughlin was born in 1784 in Riviere-du-Loop, Quebec, Canada. His father was John McLoughlin (died 1813). His mother, Angélique Fraser (1760-1842), was the eldest daughter of Scottish Canadian officer Malcolm Fraser (1733-1815); among her siblings were North West Company employee Alexander Fraser (1761-1837) and physician Simon Fraser (1769-1844).

John McLoughlin studied medicine before joining the North West Company as a surgeon and apprentice clerk. After the company merged with the Hudson's Bay Company (HBC), he became the HBC's chief factor for the Columbia Department, headquartered at Fort Vancouver in the Oregon Country (now Washington), in 1824. In this post, he traded European goods to Native people in exchange for beaver pelts. He expanded and diversified the company's operations into industries including agriculture and lumber, making the company Great Britain's foothold in the Oregon Country at a time when both the United States and Britain made claims to the region. McLoughlin also began to provide support and credit to Euro-American emigrants arriving in the Oregon Country from the east. In the 1840s, declining profits, aid to American emigrants, and other issues created tensions between McLoughlin and the HBC. Tensions also increased between McLoughlin and American emigrants, whose steady arrival had reinforced the U.S. claim to the Oregon Country. In 1846, the HBC forced McLoughlin out; he took a settlement and retired to a land claim in Oregon City, where he operated milling and mercantile businesses. That same year, the Oregon Treaty set the U.S. border at the 49th parallel. McLoughlin became a U.S. citizen in 1851, but, through congressional legislation, was also deprived of the the title to much of his property. He died in 1857, and his house in Oregon City is now the McLoughlin House Unit of the Fort Vancouver National Historic Site.

John McLoughlin had five children from two marriages. In his twenties, he had a marriage a la facon du pays ("in the manner of the country") with an Ojibwe woman with whom he had a son, Joseph McLoughlin (1809-1848); she is believed to have died not long afterward. McLoughlin later married Marguerite Waddens McKay. They had four children: John McLoughlin, Jr. (1812-1842); Marie Elisabeth "Eliza" McLoughlin (later Marie Elisabeth Eppes, circa 1814-1883); Eloisa McLoughlin (later Eloisa Rae Harvey, 1817-1884); and David McLoughlin (1821-1903).

Eloisa McLoughlin married Hudson's Bay Company employee William Glen Rae (1809-1845) and, after Rae's death, Daniel Harvey (1804-1868). William Rae and Eloisa Rae's daughter Margaret Glen Rae (1841-1912) married Theodore Wygant (1831-1905) in 1858. Theodore Wygant had emigrated to Oregon in 1850, and worked for the Oregon Steam Navigation Company (later the Oregon Railway & Navigation Company). Their daughter Nellie Amelia Wygant (1859-1940) married Martin Winch (1858-1915), who also worked for the Oregon Railway & Navigation Company, and who successfully carried out the will of his aunt Amada W. Reed to establish Reed College in Portland, Oregon.

Sources: "John McLoughlin (1784-1857), by Gregory P. Shine, Oregon Encyclopedia, https://www.oregonencyclopedia.org/articles/mcloughlin_john/; "Dr. John McLoughlin (1784-1857), Oregon History Project, https://www.oregonhistoryproject.org/articles/historical-records/dr-john-mcloughlin-1784-1857/; "McLoughlin, John (1784-1857)," by Cassandra Tate, History Link, https://www.historylink.org/File/10617; "The McLoughlin Empire and its Rulers," by Burt Brown Barker (Glendale, Calif.: The Arthur H. Clark Company, 1959); "McLOUGHLIN, JOHN (baptized Jean-Baptiste)," Dictionary of Canadian Biography, https://www.biographi.ca/en/bio/mcloughlin_john_8E.html; vital records via Ancestry.com; obituary for Theodore Wygant in the Oregonian, February 10, 1905, page 11; obituary for Martin Winch in the Oregonian, December 18, 1915, page 11.