Yaacov was born in 1912 in Bender, Moldova to Reuven and Clara Lederman. He studied law at the University of Iași, earning his J.D. in 1940. In 1933, he married Shoshana “Anna” Nathanson. He was active in Beitar, serving as the Beitar representative in Bender from 1933 to 1939.

In 1938, their son Reuven was born. In 1939, they moved to Bucharest. Despite the tumult in Romania, they managed to survive, and Yaacov continued his Revisionist and Aliyah Bet activity. In 1944, he made aliya legally (with a certificate). They embarked on the Mapilim ship Maritza as far as Istanbul, and then continued overland, by train and bus, through Turkey, Syria and Lebanon, all the way to Haifa. Upon reaching the Land of Israel, they settled in Netanya for a time. Afterwards they moved to Ramat Yitzhak, until they finally settled in Tel Aviv. Once they arrived, Yaacov joined Lehi. His cover was being a Revisionist activist and working at Leumit Health Fund.

In 1946, he was a member of the Revisionist delegation to the 22^nd Zionist Congress in Basel. From 1947 until June 1948, he resided in Paris as the Lehi representative in Europe, his cover being pursing a postdoctoral degree in law at the University of Paris. During this time, he was involved in the following activities:

• Bombing the War and Colonial Office in London from the air (this failed because the pilot went to the authorities, and the participants were arrested).
• Sending mail bombs to government officials in London
• Making contact and producing materials for intellectuals from the French left and the Soviet delegation to the UN (at the UN conference at the Palais de Chaillot)
• Recruiting into Lehi Holocaust survivors passing through Paris on their way to the Land of Israel

In June 1948, at the height of the War of Independence, he returned to the Land of Israel and was compelled to go underground once again because of the Bernadotte assassination. He surfaced again, as it were, with the other Lehi members in the beginning of 1949, after the general clemency. He was active in establishing the Fighters’ List of Lehi’s veterans.

When the party split, he joined the left wing, headed by Yellin-Mor. For his livelihood, he worked as a lawyer; he was active in pursing civil rights for Israeli Arabs. What came to be known as the Yaredor ruling was a High Court of Justice ruling based on the petition of the al-Ard organization. (This ruling is considered essential for study in all laws schools in Israel to this day.) In the 60s, he founded Semitic Action together with Uri Avnery, Natan Yellin-Mor, and Boaz Evron. He served as the editor of the movement’s publication, Etgar. After the Six-Day War, he ceased being politically active.

He passed away on 3.2.1997, leaving a wife, son and grandchildren. He was buried in Yarkon Cemetery.