Zygielbojm left home for Warsaw when he was 12, but he returned to Krasnystaw at the beginning of World War I and moved with his family to Chełm.

Stefan Starzyński, the city's president, proposed that the Jewish labor movement provide a hostage, Ester Iwińska.

[3] When the Nazis invaded Belgium in May 1940, Zygielbojm went to France and then the US, where he spent a year and a half trying to convince Americans of the dire situation facing Jews in Nazi-occupied Poland.

[3] In March 1942, he arrived in London to join the National Council of the Polish government in exile, where he was one of two Jewish members (the other was Ignacy Schwarzbart).

In London, Zygielbojm continued to speak publicly about the fate of Polish Jews, including a meeting of the British Labour Party and a speech broadcast on BBC Radio on June 2, 1942.

[5][3] On June 25, 1942, The Telegraph reported the existence of Nazi gas chambers and the mass killing of Jews, based on Szmul Zygielbojm's information.

The solidarity of the population in Poland has two aspects: first it is expressed in the common suffering and secondly in the continued joint struggle against the inhuman occupying Power.

The fight with the oppressors goes on steadily, stubbornly, secretly, even in the ghetto, under conditions so terrible and inhuman that they are hard to describe or imagine....

The Polish and the Jewish masses continue to fight together for common aims, just as they have fought for so many years in the past.

[9] In December, Karski described the conditions in the ghetto to Zygielbojm, who passed along Feiner's message: This is what they want from their leaders in the free countries of the world, this is what they told me to say: "Let them go to all the important English and American offices and agencies.

"[10] On 19 April 1943, high-ranking officials of the Allied governments of the UK and the US met in Bermuda, ostensibly to discuss the situation of the Jews in Nazi-occupied Europe.

By coincidence, that same day the Nazis attempted to liquidate the remaining Jews in the Warsaw Ghetto and met with unexpected resistance.

[12] At his home in west London, 12, Porchester Square, Paddington,[1] on 11 May Zygielbojm committed suicide with an overdose of sodium amytal, as a protest against the indifference and inaction of the Allied governments in the face of the Holocaust.

He accused the Western Allies of "looking on passively upon this murder of defenseless millions of tortured children, women and men," and the Polish government of not doing enough.

By my death, I wish to give expression to my most profound protest against the inaction in which the world watches and permits the destruction of the Jewish people.

[19][20] A granite memorial to Zygielbojm was incorporated into a building at 5 S. Dubois Street[21] in Muranów, a housing project built after World War II on the ruins of the Warsaw Ghetto.

A Bundist commander of the Warsaw Ghetto Uprising, Marek Edelman, wrote a letter that was read at the plaque's dedication.