A cobbler's apprentice in his youth, Zhekov graduated from the Military Academy in Sofia and first saw combat in the 1885 war against Serbia. He went to Italy for advanced study, returning to Bulgaria to command a regiment and then a division. During the Balkan Wars of 1912/1913, Zhekov was chief of staff of the Second Army.
World War I brought Zhekov to the top of his country's military ladder. He first served as war minister in the Cabinet of Vasil Radoslavov, August-October 1915. His chief responsibility was to ready the Bulgarian army for combat as Radoslavov hardened Sofia's ties to Berlin and Vienna and prepared to enter the conflict. When war came on October 11, Zhekov took direct command of the army.
Zhekov's forces helped shatter Serbia's defense in late 1915, but his important First Army campaigned under direct German control in the person of Field Marshal von Mackensen. The Serbian operations set an uncomfortable wartime pattern for Zhekov and his forces. Not only were substantial numbers of Bulgarian troops incorporated into Army Group Mackensen, Zhekov's concerns about Anglo- French landings in Salonika were curtly brushed aside. His call for an offensive to crush the Allied base in eastern Greece before it became a dangerous threat was vetoed by the German High Command. Bulgarian forces were left to hold most of the long Macedonian front with only minimal aid from their allies. The Bulgarians conducted a skillful offensive in August/September 1916; the defensive line was shortened and the Bulgarians took the Aegean port of Kavalla. But Zhekov also saw more of his forces abruptly detached. Once again they went to Mackensen, this time to bolster the Central Powers' offensive against Rumania in the fall of 1916.
Zhekov's conflict with the Bulgarian government over its inability to keep the Macedonian armies supplied became an open secret. So much so that opposition leaders approached the general in the fall of 1917 for aid in ousting Radoslavov and pulling Bulgaria out of the war. The move apparently struck Zhekov as premature. He betrayed the plotters to the government. But by the spring of 1918, alarmed by the internal disintegration of the army, Zhekov joined in a new effort to oust Radoslavov. The Germanophile premier fell in June, but by then the military balance in the southern Balkans had tipped perilously in favor of Bulgaria's enemies. Only Zhekov's departure for medical treatment in Germany saved him from direct responsibility for the ensuing disaster. Even so, historians have criticized him for faulty defensive positions in Macedonia during the final phase of the war. The decline of the army and unrest on the home front, however, left no one any room for optimism. Allied forces under Franchet d'Esperey burst through the Bulgarian lines at Dobro Pole in mid-September. With its fighting front broken and its army moving toward mutiny, the Sofia government hastened to conclude an armistice.
Zhekov lived in exile in the immediate postwar years. In 1923 he returned to Bulgaria to defend his wartime career. Sentenced to a long prison term, he was given amnesty after three years.
The last years of his life were devoted to quasi-Fascist politics. He led one of several ardently pro-German groups in Bulgaria before and during World War II. Zhekov hoped to come to power with the assistance of Hitler, and Berlin encouraged him with generous treatment. Zhekov was invited to tour France in 1940 to inspect the scenes of Wehrmacht victories; he also received a German pension. But the Germans refused to support Zhekov's dreams of forming his own government. The old soldier left Bulgaria at the close of World War II and died in Fiissen, Germany, October 6, 1949.
In 1913-1914 Zhekov was also part of a Bulgarian diplomatic mission to Istanbul which was involved in negotiating a military convention between Bulgaria and the Ottoman Empire. After that he served as Deputy Chief of Staff of the Bulgarian Army and commander of the 8th "Tundzha" division. In August 1915 he was promoted to major general and appointed Minister of War.