McCormick had little education. His father, Robert McCormick, was a farmer and blacksmith who invented many useful devices to use on his farm. Robert had tried to invent a reaper (a machine that harvests grain), but failed.

Cyrus McCormick invented a horse-drawn reaper that used back-and-forth-moving cutting blades and a revolving device that pushed the cut grain onto the back of the machine. He patented his "Improvement in Machines for Reaping Small Grain" on June 21, 1834. This very noisy machine is said to have scared the horses, but it made farming much more efficient.

He began to produce and sell the McCormick reaper, which was in demand by local Virginia farmers. He later opened a factory in Chicago, Illinois, and began the McCormick Harvesting Company. After a successful life, McCormick died a very wealthy man.