Yehoyachin was born on December 24,1926 in Berlin. His family made Aliyah  1934 as tourists and stayed on as illegal immigrants.

He underwent a light weapons course in Etzel on the eve of the outbreak of WWII . The course was instructed by members of the “Recruiting Company”  based at Tel-Litvinsky. During the  War, he lost touch with Etzel. In 1947 he began studying at the Hebrew University of Jerusalem and came into contact with Lehi members. Near the end of the war he was given Lehi underground assignments in the Dan Region.  Then, following an explosion which destroyed  several houses and killed many civilians on Ben-Yehuda St. Jerusalem, engineered by two British soldiers, he returned to Tel-Litvinsky, and organised a Lehi base in the area for training in weapons and field-combat, together with his friend Farchi Cohen, who’d escaped from  Jerusalem Prison. On May 29,1948,  along with all the participants and equipment of the course, he joined the IDF’s 82^nd  Battalion. During the lull in  fighting,  he moved to  Lehi’s Jerusalem  base  and served there until several days before the assassination of Bernadotte. He hid with friends in Haifa until  renewal of the battles in the Negev, then returned to the IDF as a Sergeant, responsible for the 88^th Battalion’s Recconnaissance Unit. In 1956, after completing  his studies at the Hebrew University and in Switzerland, he left the country. He studied Economics in various universities in England, Africa and Asia, and was working  with international organisations until 1972. From then, until retiring in 1996, he worked as a Professor of Economics at the University of Utrecht, in the Netherlands. He had written about a dozen books about Economics, General History and Society, and two novels about the land of Israel between 1934 and 1956. Yehoyachin is married to Nancy Golomb. They have two children and three grand-daughters.