Sigma Nu was founded in 1869 by 3 men on the principles of Love, Truth, and Honor and against the childish hazing then present at VMI. Sigma Nu is a part of the Lexington Triad (the other two are Alpha Tau Omega and Kappa Alpha Order (which shouldn't be confused with Kappa Alpha Society). Sigma Nu was one of the forces behind the Select 2000 Initiative, and was the first fraternity to implement a risk reduction policy.

The Founders of Sigma Nu, Mr. James Frank Hopkins, Mr. Greenfield Quarles, and Mr. James McIlvaine Riley Jr., met one evening after Bible study at the house of the Superintendent of VMI at a limestone outcropping near the modern-day parade grounds. They were all upperclassmen, and had already passed through the rat period at VMI. Two of them had served in the Civil War, and knew the difference between military discipline and hazing. They committed to helping other men see the light and turn away from another fraternity at VMI which hazed men until they joined. Founder Hopkins was a Mason, and it is said that the Ritual of Sigma Nu has similarities to the Masonic York Rite.