Born at Tunyogmatolcs, Austria-Hungary to a family of Hungarian Jews, he attended Polgári Iskola (high school) in Mátészalka, which was later renamed in his honor. (The name was later changed after the fall of the Communist regime).
Hungary in World War I
When he was 18, Zalka lied about his age in order to volunteer in the Hungarian Army. Officer of hussars Zalka fought in Italy, which later became the subject of his novel Doberdó. He went to battle on the Russian front in 1917 and ended up in a Russian prisoner of war camp, where he was influenced by Communism.
Russian Civil War
In February 1918, during the Russian Civil War, Zalka formed an international group of Red Guards in Khabarovsk which mainly comprised ex-prisoner Hungarians, and participated in the punitive operations in Siberia against the White formations. At the end of World War I, Zalka chose to stay in Russia instead of returning to Hungary. Zalka met his Russian future wife Vera. They had one daughter, who later died due to complications from the accident at Chernobyl.
GPU operational activities
In 1920, Zalka fought against Poland in the Battle of Kiev. From 1921 to 1923, he was commander of a regiment of cavalry of the VCK GPU, the Soviet Communist Party Secret Service, that fought in Crimea and Ukraine, and was involved in the elimination of forces of Nestor Makhno and other atamans of Ukraine. Because these atamans met with widespread support of local people, many of the actions resulted in punitive operations against civilians. At some point, he fought in the Turkish War of Independence under the assumed name of Lukács Tábornok (General Lukács).
While he was in the prisoner of war camp, he organized the prisoners´ theatre. He was director of the "Theatre of Revolution" (now called "Mayakovsky Theatre") in Moscow (1925–1928).
Spanish Civil War
In 1936, he moved to Spain, where in November 1936 he joined the International Brigades to fight in the Spanish Civil War. Under the assumed name of Pavol Lukács and with the rank of General, he commanded initially the XII International Brigade and then the 45th Division. In 1937, his car was hit by artillery fire and he was killed near Huesca. Zalka is mentioned in a number of works of Hemingway.
His remains were originally buried in the south of Spain but decades after his death, Zalka's nephew (who also fought in the Spanish war) was invited by the Spanish royal family to a ceremony celebrating the end of the civil war. At this point, he was able to carry Zalka's remains to Hungary where they were buried in a military cemetery in Budapest along with other high-ranking Hungarian military officers.