Korczak was born in Warsaw in 1878.
He was unsure of his birth date, which he attributed to his father's failure to promptly acquire a birth certificate for him.
His parents were Józef Goldszmit, a respected lawyer from a family of proponents of the haskalah, and Cecylia née Gębicka, daughter of a prominent Kalisz family.
Born to a Jewish family, he was an agnostic in later life who did not believe in forcing religion on children.
His father fell ill around 1890 and was admitted to a mental hospital, where he died six years later on 25 April 1896.
Spacious apartments were given up on Miodowa street, then Świętojerska.
As his family's financial situation worsened, Henryk, while still attending the gymnasium (the current 8th Lycée in Warsaw), began to work as a tutor for other pupils.
In 1896 he debuted on the literary scene with a satirical text on raising children, Węzeł gordyjski (The Gordian Knot).

In 1898, he used Janusz Korczak as a pen name in the Ignacy Jan Paderewski Literary Contest.
The name originated from the book Janasz Korczak and the Pretty Swordsweeperlady (O Janaszu Korczaku i pięknej Miecznikównie) by Józef Ignacy Kraszewski.
In the 1890s he studied in the Flying University.
During the years 1898–1904 Korczak studied medicine at the University of Warsaw and also wrote for several Polish language newspapers.
After graduation, he became a pediatrician.
In 1905−1912 Korczak worked at Bersohns and Baumans Children's Hospital in Warsaw.
During the Russo-Japanese War, in 1905–06 he served as a military doctor.
Meanwhile, his book Child of the Drawing Room (Dziecko salonu) gained him some literary recognition.

In 1907–08, Korczak went to study in Berlin.
While working for the Orphans' Society in 1909, he met Stefania Wilczyńska, his future closest associate.
In 1911–1912, he became a director of Dom Sierot in Warsaw, an orphanage of his own design for Jewish children.
He hired Wilczyńska as his assistant.
There he formed a kind-of-a-republic for children with its own small parliament, court, and a newspaper.
He reduced his other duties as a doctor.
Some of his descriptions of the summer camp for Jewish children in this period and subsequently, were later published in his Fragmenty Utworów and have been translated into English.

During World War I, in 1914 Korczak became a military doctor with the rank of lieutenant.
He served again as a military doctor in the Polish Army with the rank of major during the Polish-Soviet War,  but after a brief stint in Łódź was assigned to Warsaw.
After the wars, he continued his practice in Warsaw.
Korczak was born in Warsaw in 1878. He was unsure of his birth date, which he attributed to his father's failure to promptly acquire a birth certificate for him. His parents were Józef Goldszmit, a respected lawyer from a family of proponents of the haskalah, and Cecylia née Gębicka, daughter of a prominent Kalisz family. Born to a Jewish family, he was an agnostic in later life who did not believe in forcing religion on children. His father fell ill around 1890 and was admitted to a mental hospital, where he died six years later on 25 April 1896. Spacious apartments were given up on Miodowa street, then Świętojerska. As his family's financial situation worsened, Henryk, while still attending the gymnasium (the current 8th Lycée in Warsaw), began to work as a tutor for other pupils. In 1896 he debuted on the literary scene with a satirical text on raising children, Węzeł gordyjski (The Gordian Knot).
In 1898, he used Janusz Korczak as a pen name in the Ignacy Jan Paderewski Literary Contest. The name originated from the book Janasz Korczak and the Pretty Swordsweeperlady (O Janaszu Korczaku i pięknej Miecznikównie) by Józef Ignacy Kraszewski. In the 1890s he studied in the Flying University. During the years 1898–1904 Korczak studied medicine at the University of Warsaw and also wrote for several Polish language newspapers. After graduation, he became a pediatrician. In 1905−1912 Korczak worked at Bersohns and Baumans Children's Hospital in Warsaw. During the Russo-Japanese War, in 1905–06 he served as a military doctor. Meanwhile, his book Child of the Drawing Room (Dziecko salonu) gained him some literary recognition. 
In 1907–08, Korczak went to study in Berlin. While working for the Orphans' Society in 1909, he met Stefania Wilczyńska, his future closest associate. In 1911–1912, he became a director of Dom Sierot in Warsaw, an orphanage of his own design for Jewish children. He hired Wilczyńska as his assistant. There he formed a kind-of-a-republic for children with its own small parliament, court, and a newspaper. He reduced his other duties as a doctor. Some of his descriptions of the summer camp for Jewish children in this period and subsequently, were later published in his Fragmenty Utworów and have been translated into English.
During World War I, in 1914 Korczak became a military doctor with the rank of lieutenant. He served again as a military doctor in the Polish Army with the rank of major during the Polish-Soviet War,  but after a brief stint in Łódź was assigned to Warsaw. After the wars, he continued his practice in Warsaw.
Janusz Korczak