Leo Bretholz was born the eldest child in a family of Polish Jewish immigrants in Vienna, Austria. His father Max Bretholz died when Leo was nine years old, and his mother Dora supported the family by working as a seamstress. After the Nazi Anschluss (annexation) of Austria in 1938, his relatives and neighbors were arrested, and his mother urged him to leave the country. His life on the run for the next several years involved a series of daring escapes from death. He took a train to Trier, Germany, and swam across the Sauer River into Luxembourg. From there, he went to Antwerp, Belgium, where he began training to become an electrician. In 1940, when Germany invaded Belgium in World War II, he was deported to the St. Cyprien internment camp in France. He escaped by crawling under the fence. In 1942, he was arrested and sent to the Drancy camp. When he was being deported by cattle car to the death camp at Auschwitz, he and a friend managed to pry open the bars of a window and jump off the moving train. Upon crossing into the southern (Vichy) zone of France, he was arrested again and spent nine months in prison. In October 1943, he was being sent to the Atlantic coast for forced labor, when he again escaped from the train. In Toulouse, he joined the Resistance, forging identification papers and scouting Germans. After the Allied invasion of D-Day in June 1944, Leo assisted refugees in France until the end of the war. His mother, sisters and 55 other relatives all perished in the Holocaust. In 1947, he emigrated to the USA and settled in the Baltimore, Maryland area. He married Florine Cohen, with whom he had three children. Leo worked for much of his career in sales, and later managed bookstores.
In 1998, he published a memoir, Leap into Darkness: Seven Years on the Run in Wartime Europe, written with Michael Olesker. He spoke about his experiences during the war in schools, and was a witness at Congressional hearings on legislation that would have permitted Holocaust survivors to sue the French National Railway (SNCF) in American courts.