The Crown Prince served most of the pre-war years with the 1. Foot Guards Regiment in Potsdam, but he also commanded a Leib-Hussar regiment in Danzig under the noted Totenkopf commanding general August von Mackensen. For a few months immediately prior to the war, Willy was also in service with the Great General Staff in Berlin. He married Duchess Cecelie zu Mecklinburg, with whom he had four sons and two daughters. His eldest child Wilhelm served as First Lieutenant during the Second World War and was mortally wounded during fighting at Valenciennes, France.

As war broke out in early August 1914, the 32-year old princely lieutenant general was given command of the Fifth Army which was tasked with holding the French in check along the Western Front's southern flank. Granting command of a field army to a crown prince was also a time-honored Hohenzollern tradition. Although Willy was a leader with sound insight and fairly good instincts, he did nonetheless have a dubious reputation as a commander -- the Allies ridiculed him as an imbecile -- but his early successes in the Ardennes helped change this reputation somewhat. His troops early on were able to capture the fortress at Longwy, and he was awarded a much-coveted Pour le Merite in 1915 for his leadership and valor. His insistence on going on the offensive and charging into Lorraine, however, also forced Chief of Staff von Moltke to transfer some northern flank divisions to the south, thus altering the von Schlieffen Plan.

Crown Prince Wilhelm's troops were also engaged at Verdun in 1916, an experience which caused him to begin to see the senselessness of the war. He thereafter was charged with leading Army Group Deutscher Kronprinz which in 1918 had some noteworthy successes along the Aisne-Champagne front. He continued to become more disillusioned about Germany's prospects and in vain campaigned Supreme Headquarters to pursue a policy of retreat.

As the war ended, the young general followed his father into exile in the Netherlands, living on the island of Wieringen in the Zuiderzee and officially renouncing any right to the throne. In 1923, he returned to his wife Cecilie at their home in Potsdam where he began rubbing shoulders with some of the Nazi leadership, including Hitler himself. The German government paid an allowance to Willy and his brothers but threatened to cut them off should they ever speak out against the Nazis. Hitler's promise to the Crown Prince that that he would eventually restore the monarchy was of course never to take place. Willy remained a civilian during World War Two, but he was placed under arrest by the French for a short time after the war. Shortly after moving to Hohenzollern Castle in Hechingen Baden-Württemburg, the erstwhile crown prince and army commander died of a heart attack in 1951. He is laid to rest there in the St. Michaels-Bastei.