Alexander Hays was born on July 8, 1819, in Franklin, Pennsylvania. After attending two academies, he studied at Allegheny College. In his senior year, he left Allegheny to go to the US Military Academy at West Point. Hays graduated in 1844, after forming a close friendship with Ulysses S. Grant, who graduated in 1843.

 For his service in the Mexican War, Hays received a brevet. In 1848, Hays resigned from the army, traveling to California in search of gold. He later returned to Pennsylvania and became a successful construction engineer with a specialty in building bridges.

When the Civil War began, Hays enlisted in the Regular, as captain of the new 16th Infantry. He commanded the 63rd Pennsylvania, and commanded the regiment in Maj. Gen. Philip Kearny's division of the III Corps. Hays took part in the Battles of Yorktown, Williamsburg, Seven Pines, Savage's Station and Malvern Hill. In the Second Battle of Bull Run, he was seriously wounded. On September 29, 1862, he was promoted to Brigadier General, and was stationed in the defenses of Washington when he had recovered.

In 1863, he led the 3rd Division of the II Corps, which took part in Pickett's Charge. Hays also participated in the Battle of Gettysburg. When the III Corps joined the II Corps, Hays was assigned to brigade command. Hays was killed in combat at the Battle of the Wilderness, on May 5, 1864. General Hays' battles are recounted on his magnificent monument.

It was he who gave the names to the Mexican War Streets he laid out in Allegheny City (now Pittsburgh's North Side). The combination of inverted cannons and the granite artistry of Peter Charles Reniers was erected by the men who served under Hays.

On the day of his funeral, businesses closed, the streets filled with people, and cannon fire sounded from the hills. During his 1869 Presidential visit to Pittsburgh, President Grant personally requested to be taken to the grave of his fallen comrade. After once circling the monument in contemplative silence, he sat upon an inverted cannon and wept openly.