• Commander of the Palmach Yitzhak Sadeh, 1890

 

Sadeh was awarded a medal from the Russian army for his bravery during World War I. Between 1917 – 19, he assisted Joseph Trumpeldor in the founding of HeHalutz (The Pioneer) movement. In 1920, Sadeh made aliyah to Eretz Israel, where he became one of founders and leaders of Gdud HaAvoda (The Work Battalion).

In 1921, Sadeh was a Haganah (Defense) commander in Jerusalem. During the 1929 riots he took part in the battle defending Haifa. When the 1936 – 1939 Arab revolt in Palestine began, Sadeh established the Nodedet (Wandering Troop or Patrol Unit) in Jerusalem, that confronted the Palestinians in their villages and bases. He demanded that his troops "leave the defenses" and initiate military operations.

In the summer of 1937, as commander of the Jewish Settlement Police, he founded the FOSH (Hebrew abbreviation, FO'SH, for Plugot Sadeh, lit. Field Companies), the commando arm of the Haganah. It was an elite Jewish strike force, whose members were hand picked by Sadeh. The force was established during the Great Arab Revolt in what at the time was the British Mandate of Palestine.

Among other activities, Sadeh commanded the establishment of Kibbutz Hanita on an isolated hill on the southern border of Lebanon. In 1941, he was instrumental in the founding of the Palmach (acronym for Plugot Mahatz, the Haganah's enlisted military forces of volunteers). The purpose of this clandestine elite unit was to prepare to undertake a guerilla war in the event of the Axis forces entering Palestine. During the 200 days of dread, Sadeh worked on the Carmel Plan, which was a detailed strategy to withdraw the entire Jewish community in Palestine to Carmel, forming a giant enclave to withstand the invaders.

He was Commander of the Palmach until 1945, when he was appointed as the Haganah's Chief of the General Staff and, among other activities, was in charge of the movement's operations against the British Forces during the British Mandate of Palestine and in operations that brought clandestine Jewish immigrants to Israel. He was also instrumental in founding the Gadna in 1941, and became the program's first unofficial commander.

At the beginning of 1948 Yitzhak Sadeh was in commanded of Haganah training camp at Mishmar Ha'emek. In early April he successfully defended the kibbutz against a full scale attack by the Arab Liberation Army. In the counter attack that followed his troops conquered a large section of the Jezreel Valley. At the end of April he commanded two Brigades in a series of attacks on strategic areas in and around Jerusalem, Operation Yevusi.

During the truce in June he was responsible for the establishing the first armored brigade of the IDF. In July this Brigade played an important part in Operation Danny, capturing Lod airport, and in October, Operation Yoav, the taking of the Iraq Suwaydan fortress blocking the road to the Negev. In December 1948 he participated in Operation Horev in the Negev, when the forces under his command crossed the Egyptian border and threatened El-Arish as well as the Egyptian army in the Gaza Strip.

When the War of Independence ended and the Palmach was dismantled in 1949, Sadeh left military service. He wrote essays, stories and plays. The book Misaviv Lamedura (Around the Bonfire) includes a collection of articles he wrote under the pen name Y. Noded (Y. Wanderer).

Prior to his death in August 1952, he had become a charismatic and colorful figure, whose nickname in the Palmach was HaZaken (The Old Man). He is buried at Kibbutz Givat Brenner.

Sadeh was a promoter and educator in the field of Jewish sport. When in Russia, he participated in wrestling meets and became the wrestling champion of St. Petersburg. As an active sportsperson, he recognized physical education as having important cultural and educational values. As a member of the Hapoel (The Worker) board, he set policies and established guidelines and created the Hapoel motto, Alafim lo Alufim (Thousands not Champions). Today, thousands of sports people and soldiers take part in the Mount Tavor Race, devoted to the Sadeh's ideals.

• The Yitzhak Sadeh Prize for Military Literature is given annually in his honor.
• The Israel Postal Service issued a stamp commemorating Sadeh.
• The kibbutzim Nir Yitzhak and Mashabei Sadeh in the Negev are his namesakes, as is moshav Sde Yitzhak and numerous streets throughout Israel (often named Aluf Sadeh, literally "General Sadeh").

In 2005, he was voted the 121st greatest Israeli of all time, in a poll by the Israeli news website Ynet to determine whom the general public considered the 200 Greatest Israelis.