Haber, the son of a merchant, was born at Breslau, now Wrocław in Poland. He was educated at Berlin, Heidelberg, Charlottenburg, and Jena, and in 1894 he became an assistant in physical chemistry at the Technical Institute, Karlsruhe, where he remained until 1911, being promoted to a professorship in 1906. He moved to Berlin in 1911 to become director of the Kaiser Wilhelm Institute of Physical Chemistry. Though an intensely patriotic German he was also a Jew and with the rise of anti-Semitism he resigned his post in 1933 and went into exile in England, where he worked at the Cavendish Laboratory, Cambridge. He died in Basel en route to Italy.

Haber is noted for his discovery of the industrial process for synthesizing ammonia from nitrogen and hydrogen. The need at the time was for nitrogen compounds for use as fertilizers – most plants cannot utilize free nitrogen from the air, and need ‘fixed’ nitrogen. The main source was deposits of nitrate salts in Chile, but these would have a limited life.

Haber, in an attempt to solve this problem, began investigating the reaction: N₂ + 3H₂ ≡ 2NH₃

Under normal conditions the yield is very low. Haber (1907–09) showed that practical yields could be achieved at high temperatures (250°C) and pressures (250 atmospheres) using a catalyst (iron is the catalyst now used). The process was developed industrially by Carl Bosch around 1913 and is still the main industrial method for the fixation of nitrogen. Haber received the Nobel Prize for chemistry for this work in 1918.

During World War I, Haber turned his efforts to helping Germany's war effort. In particular he directed the use of poisonous gas. After the war he tried, unsuccessfully, to repay the indemnities imposed on Germany by a process for extracting gold from seawater.