Kalergis was born in Lowell, Massachusetts on January 13, 1917. Kalergis enlisted in the U.S. Army in February 1941, prior to the start of World War II. He was commissioned as a lieutenant after attending the Field Artillery Officer Candidate School at Fort Sill, Oklahoma in 1942.

He served as an artillery officer with the 882nd Field Artillery Battalion. By November 1943, he was a captain and battalion adjutant and promoted to major shortly after the unit arrived in France in February 1945. He was awarded the Bronze Star while with the 882nd which generally supported the 70th Infantry Division's 274th Infantry Regiment during the Rhineland and Central Europe campaigns.

From 1949 to 1952, Kalergis, as a major, was assistant professor of military science and tactics at Saint Bonaventure College, a Franciscan school in St. Bonaventure, New York.  As a lieutenant colonel in 1954, Kalergis commanded the 36th Field Artillery Group's 597th Armored Field Artillery Battalion in Hanau, Germany. In the in 1960s, Kalergis served tours in South Korea and as commander of 2nd Armored Division (United States) at Fort Hood, Texas.

During the Vietnam War from 1967 to 1968, he commanded the artillery for the corps-level organization I Field Force, Vietnam (United States). The next year, he served as First Field Force's chief of staff.  In Vietnam, he was recognized in efforts to quantify and reduce "harassment and interdiction fire", artillery fire intended to reduce enemy morale and movement. Yet in practice, it was rarely observed or checked for results and generally proved useless in countering enemy activities in a war without fronts.

Kalergis developed systems to quantify and significantly reduce its use due to ineffectiveness, collateral damage to civilians and its high cost. As a major general, Kalergis was Deputy Commanding General for Logistical Support of the United States Army Materiel Command from 1970-1972. In early 1972, Kalergis was recognized for his organizational abilities and tasked with drawing up the 1973 reorganization of the U.S. Army, the most extensive reorganization of the Army in the continental United States since 1942.

Operation STEADFAST resulted in the establishment of U.S. Army Forces Command (FORSCOM) and U.S. Army Training and Doctrine Command (TRADOC).  It was followed by subsequent reorganizations in Army Staff Headquarters and of units in the field. The effort to accomplish internal reorganization was initiated with the Army, forestalling efforts by the executive or legislative branch in the post-Vietnam era.  

Kalergis then served as assistant vice chief for Army Chief of Staff. From 1974 until his retirement from active duty in 1975, Kalerigis was commanding general of the First United States Army at Fort Meade, Maryland.

Kalerigis died of cancer at Walter Reed Army Medical Center on April 13, 1991.