Ben-Gal was born 1936 in Lodz, Poland. When he was three years old, World War II broke out with Germany invading Poland. The family fled to Russia and were sent to Siberia. After Yanush's mother died in Siberia, his father decided to save 3-year old Yanush and his 6 year-old sister Liana by bribing some Polish officials to take the youngsters to safety with the Polish Anders' Army. The siblings first ended up in Tehran, then they were sent to India. Together, they walked, hitchhiked, and hitched rides aboard trains, and after many adventures and hardships they arrived in British Mandatory Palestine (later Israel) with a group of German-Jewish refugee children. They were placed in a kibbutz, like many European orphans escaping the Holocaust, but soon left the kibbutz and hiked to Tel Aviv, where they were taken in and raised by a distant cousin.
A few years after Israel became independent and won the 1948 Arab-Israeli War, Ben-Gal was drafted into the Israel Defense Forces (IDF). His first combat experience came during the 1956 Suez War with Egypt. Despite having dreamed of being a doctor, he decided to stay in the army after his mandatory military service was finished. In an interview, he explained his reasons:
"I never intended to turn the army into a career, but I remained because I liked it. I loved the Negev, the desert, the fields. I loved speeding in jeeps. Later I got used to the army, and it became a part of me. And maybe also, I was afraid to make a new start in life."
During the Six-Day War in 1967, he was the operations chief of a brigade that broke through Egyptian fortifications in the Sinai. He lost half his right foot when his jeep struck a mine. By 1972, he had been appointed commander of a brigade.
During the Yom Kippur War in 1973, Ben-Gal commanded the 7th Armored Brigade and oversaw the defense of the Golan Heights against Syrian attack. Ben-Gal had foreseen the war two weeks before it started, and had begun preparing his brigade. As the threat of war wasn't being taken seriously in Israel at the time, he had been branded a "madman". However, when the war broke out, his brigade was the only IDF unit in a state of full readiness.
In June 1997 he was called to testify in a libel suit that Ariel Sharon brought against the Israeli newspaper Ha'aretz for their claim that he had concealed his plans for an operation into Lebanon in 1982 - during which Ben Gal was still leading the Northern Command. His testimony at trial, however, contradicted earlier statements he had made at Tel Aviv University where he stated that the greatest problem with the Lebanon War was the ""secret, unapproved plan of the defense minister and chief of staff."" 
The following month Ha'aretz requested that the Attorney General investigate the possibility that Ben-Gal had given false testimony in court in exchange for business favours from Sharon. The complaint noted that shortly before his appearance at the trial, Ben-Gal was sent by Sharon to explore the possibility of a large natural gas deal in Russia.
From 1996 to 2002 he was Chairman of the Board of Directors for Israel Aerospace Industries. He also serves on the board for the International Policy Institute for Counter-Terrorism.
During a 2007 military conference in Latrun, Ben-Gal sharply criticized what he viewed as a deterioration in the battle readiness of the IDF, and claimed that the IDF's technological revolution has turned soldiers into "bionic machines" and sewn fear among senior officers that open criticism would hamper advancement in their own careers. He expressed the view that all the new technologies being introduced were useless, and claimed that it had gotten to the point where commanders prefer to email each other instead of interacting.
Since 2009 he has been serving as Chairman of the Board of Directors for N.S.O Group Technologies.
- "At 3, He Walked Across Russia; Still Tough, General Ben-Gal Commands the Drive into Lebanon", People, Mira Avrech, April 03, 1978, Vol. 9, No. 13
- The Yom Kippur War: The Epic Encounter That Transformed the Middle East, Volume 2004, Part 2, Abraham Rabinovich, Random House, Inc., 2005, ISBN 978-0-8052-1124-5
- "The Yom Kippur War 1973: The Golan Heights", Simon Dunstan, Howard Gerrard, Illustrator Kevin Lyles, Howard Gerrard, Osprey Publishing, 2003, ISBN 978-1-84176-220-3
- A portrait of the Israeli soldier, Reuven Gal, Greenwood Publishing Group, 1986, ISBN 978-0-313-24315-8
- Israel's Lebanon War, Ze'ev Schiff, Ze'ev schiff/ehud ya'ari, Simon and Schuster, 1985, ISBN 978-0-671-60216-1
- Righteous victims: a history of the Zionist-Arab conflict, 1881-1999, Benny Morris, Random House, Inc., 1999, ISBN 978-0-679-42120-7
- "Ariel Sharon denies accusation of influencing witness", J Weekly, February 19, 1999