Born in Warsaw in a Jewish family of Sephardi origin, Landsberg was descended from Salomon Calahorra, the royal physician of two kings of Poland: Sigismund II Augustus and Stephen Báthory.
Hilel was the son of Mendel Lewkowicz Landsberg, a tradesman in Warsaw, and Lea née Lewek.
Hilary Landsberg married Hana Mendelsburg (1838–1904) and had two sons Alexander (Abram Lajb) (1858–1924) and Felix (Fishel) (1868–1923), and six daughters.
In 1857, Landsberg started a small cloth-manufacturing business in Tomaszów Mazowiecki with ten hand-looms.
In 1881–1883 he constructed a large textile factory in the town (Gustowna street 46), introducing steam power.