Joseph Trumpeldor was born in Pyatigorsk in the North Caucasus of the Russian Empire. His father, Wulf Trumpeldor, served as a cantonist in the Caucasian War, and as a "useful Jew", was allowed to live outside the Pale of Settlement. Though proudly Jewish, Trumpeldor's upbringing was more Russian than traditionally Jewish. Originally in training as a dentist, Joseph Trumpeldor volunteered for the Russian army in 1902. During the Russo-Japanese War, he participated in the siege of Port Arthur, where he lost his left arm to shrapnel. He spent a hundred days in the hospital recovering, but elected to complete his service. When he was questioned about his decisions and told that he was heavily advised not to continue fighting given his handicap, he responded "but I still have another arm to give to the motherland." When Port Arthur surrendered, Trumpeldor went into Japanese captivity. He spent his time printing a newspaper on Jewish affairs and organized history, geography and literature classes. He also befriended several prisoners who shared his desire of founding a communal farm in Palestine. On return from captivity, he moved to St. Petersburg. Trumpeldor subsequently received four decorations for bravery including the Cross of St. George, which made him the most decorated Jewish soldier in Russia. In 1906 he became the first Jew in the army to receive an officer's commission.
Due to his handicap he began to study law. He gathered a group of young Zionists around him and in 1911 they emigrated to Palestine, then part of the Ottoman Empire. At first he joined a farm on the shore of the Sea of Galilee, and then worked for a time at Kibbutz Degania.