Jaretzki was born in New York City to Alfred Jaretzki, a leading
corporate lawyer, and Tillie Shire Jaretzki on November 17, 1892. Alfred Jaretzki, Sr. worked as a partner at
Sullivan & Cromwell, an international corporate law firm founded by
Algernon Sydney Sullivan and
William Nelson Cromwell. Jaretzki, Sr. took over the role of managing partner of Sullivan & Cromwell from Cromwell in 1900. After graduating from
Morristown School (now Morristown–Beard School) in
Morristown, New Jersey, Jaretzki completed his bachelor's degree at
Harvard University in
Cambridge, Massachusetts, in 1913. He then earned a law degree at
Harvard Law School in 1916. Jaretzki earned admittance to the
Bar association that year. While at Harvard, Jaretzki served as a member of the Editorial Board of the
Harvard Law Review. He also played on the
lacrosse team and participated on the
debate team. In 1916, Jaretzki joined Sullivan & Cromwell as a partner. He later rose to the position of senior partner at the firm. Jaretzki served at Sullivan & Cromwell during the same period as
John Foster Dulles. ==Service during World Wars I and II==