Born in Newry, Ireland on June 11, 1846, Leif Newry Fitzroy Crozier served as a militia officer and North-West Mounted Police (NWMP) officer. The Crozier family settled in Belleville, Upper Canada in the 1860s. Despite articling as a lawyer and training as a doctor, Crozier pursued a military career and was appointed a sub-inspector of the newly created mounted police force in 1873. He rose rapidly through the ranks and was one of six NWMP superintendents by 1876.
In the fall of 1878, Crozier was given command of Fort Walsh, the most important and volatile NWMP post, as Sitting Bull and 5,000 Sioux were camped roughly 150 miles to the east. He urged the refugees to return to the United States on several occasions, but they ignored his instructions. Shortly before Sitting Bull's eventual surrender, Crozier was transferred to Fort Macleod. In May 1884, he took command of the detachment at Battleford where dissatisfaction and militancy were growing among the area's Métis and Cree.
On March 13, 1885, Crozier warned Lieutenant-Governor Edgar Dewdney about the likelihood of a Métis rebellion. On March 26, he ignored approaching reinforcements and led a group of about 100 Mounted Police and volunteers out of Fort Carlton. Crozier and his men encountered a superior force of Métis on the Carlton Trail north of Duck Lake, which led to the opening engagement of the North-West Resistance. Crozier's force suffered serious casualties during the short battle as nine volunteers and three police were killed. Despite his impetuous leadership, Crozier was promoted to assistant commissioner of the NWMP on April 1. He returned to his post at Battleford and was transferred to headquarters in Regina in 1886.
Crozier resigned from the NWMP in June 1886 after being passed over for the position of commissioner. He later moved to the United States where he established a general store at Cushing, Oklahoma. Leif Crozier died there on February 25, 1901, and was buried in Belleville.