His father Aleksander Rajchman was a journalist specialized in theatre and music critique, who in the period 1882-1904 was the publisher and editor-in-chief of the artistic weekly Echo Muzyczne, Teatralne i Artystyczne and was co-founder and first director of the National Philharmonic in Warsaw in the years 1901–1904.

Rajchmans ran a social salon who hosted many Polish artists of their times, in particular Eliza Orzeszkowa, Maria Konopnicka, and Zenon Pietkiewicz.

His older sister a Polish independence activist and historian of education Helena Radlińska was the founder of Polish social pedagogy, his older brother a physician and bacteriologist Ludwik Rajchman was the world leader in social medicine and director of the League of Nations Health Organization, the founder of the United Nations International Children's Emergency Fund (UNICEF) and its first chairman in the years 1946–1950.

His nephew a Polish-American electrical engineer Jan A. Rajchman was a computer pioneer who invented logic circuits for arithmetic and magnetic-core memory to result in development of high-speed computer memory systems and whose son John Rajchman is a noted American philosopher of art history, architecture, and continental philosophy.

His first cousin a microbiologist and serologist Ludwik Hirszfeld co-discovered the heritability of ABO blood group type and foreseen the serological conflict between mother and child.