Along with his elder brothers Cyrus and William, he is regarded as one of the fathers of modern agriculture due to his part in the development of the McCormick Reaper and what became the International Harvester Company.

He also owned and developed vast amounts of real estate in downtown Chicago and Lake Forest, Illinois.

He was raised at the family homestead known as Walnut Grove, near Raphine in Rockbridge County, in the Shenandoah Valley on the western side of the Blue Ridge Mountains.

In fall 1848, he moved to Chicago with his wife and infant son to join Cyrus in setting up an even larger factory.

Brother William joined them in 1850 in a business in run by Cyrus to manufacture reapers and sell them across the midwestern United States.

They created what eventually became known as the McCormick Harvesting Machine Company, with Leander taking over management of the manufacturing department, which he controlled for the next 30 years.

[3] At the time of his death in 1900, he had extensive holdings in downtown Chicago, and a stock farm in Lake Forest, Illinois.

[4] On October 22, 1845, at age 26, McCormick married Henrietta Maria Hamilton at her parents' homestead, Locust Hill, in Rockbridge County.