He was the last of five children; his eldest brother Edward Byron LaMoure was killed during an Indian raid in Elk Point, Dakota Territory on August 9, 1865.

He came to Davenport, Iowa on March 2, 1859, in 1860 he joined a rush of gold-seekers to Pike's Peak but turned back east during the Fall of that year without striking gold.

In 1862 he settled in Elk Point, Dakota Territory, while there LaMoure was engaged in a Transportation business with H. D. Booge & Co.; he became familiar with the Brulé Sioux and received an appointment as their sub-agent in 1865.

In 1870 LaMoure gave up his connection to the Indians and relocated to Pembina County, Dakota Territory, where he became a merchant in Neche, a business he continued for many years.

In 1873, LaMoure led a rescue party into a horrific blizzard to find and save a group of laundry women and small children accidentally left behind by George Armstrong Custer when the 7th Cavalry apparently got lost in a whiteout.