He was born into a family of Orthodox Jews, and his father was a rabbi in Żółkiewka near Lublin. It is not known what education Leon Feldhendler received, or what exactly he did before World War II. In May 1935, he married Toba Wajnberg, and in October of the same year his first son, Chaim, was born.

When war broke out, in 1940 Leon Feldhendler headed the Jewish Council (Judenrat) in Żółkiewka, which was established by the Germans. Two years later, he also became chairman of the local branch of the Jewish Self-Help Society, making him the leader of the Jewish community.

When Operation Reinhardt began and the first transports of Jews left for the Sobibór and Bełżec camps, Leon Feldhendler tried to protect his loved ones, but in October 1942 all the remaining Jews, including members of the Judenrat and their families, were herded to the transit camp in Izbica, which was located about 20 kilometers from Żółkiewka. There, after a few days, some of Leon Feldhendler’s family was shot. Those who survived hid in the Izbica ghetto for another two weeks, but were later discovered and taken to Sobibor. On the ramp, Leon Feldhendler was pulled from the crowd by his cousin, then a camp inmate, and taken to work. The rest of the family, including his sisters, brother, wife and children, were led to the gas chamber and murdered.

It is not known exactly what Feldhendler’s own daily life was like. He was one of 700 prisoners who worked at the camp. Those who survived the hell of Sobibor often recalled Feldendler. One of them was Aron Licht:

After a hard roll call we fall into bed (…) it fell to me to sleep next to Leon Feldhendler. I can’t fall asleep. I start a quiet conversation with Leon. “What’s going to happen?” He answers me firmly, “What is to be? You see, brother, what the situation is like: hard working, hungry. But this is not their goal. We live until we get sick and then into the oven (…) and that’s how the Jewish people perish.”

In turn, the other leader of the later Sobibor revolt, Alexander Peczerski, recalls the moment he met Leon Feldhendler as follows:

It was a sunny, warm day. I went out with a few comrades from our barrack to the courtyard (…) a stocky Jew of medium height, about 40 years old, squatted down. He had recently returned from work (…) our interviewee was an old camp inmate. His work consisted of sorting through the belongings of those killed. He knew a lot. (…) in simple words, as if it was about ordinary, everyday things, he told us about the camp, and we, the newcomers (…) listened to his account with horror.

The two prisoners met frequently for talks. It was probably then that the idea of organizing a revolt emerged. Everything was meticulously planned and the uprising began on October 14, 1943. A strictly selected group, including Peczerski and Feldhendler, lured Germans to one of the sheds on any pretext and killed them there, seizing their weapons. 12 SS men and 2 Ukrainian guards were killed in this way. Unfortunately, someone from the crew found one of the bodies and raised the alarm. The prisoners rushed into open combat. Hundreds of them were killed by the guards’ machine guns or in the minefield surrounding the camp, but more than 300 prisoners escaped from the camp. Only 61 of them survived the war.

Leon Feldhendler escaped and was initially hidden by the Polish population in the village of Maciejow Stary. Then, when the Red Army took over Lublin, he went to the city and settled in the former ghetto.

In February 1945, he married Estera Muterperel, 20, but two months later the Sobibor escapee was shot dead in his apartment in unexplained circumstances.