In 1908 he obtained his postdoctoral degree under the supervision of Jan Rozwadowski on the basis of the work Relationships of the Lechitic languages kinship.

In 1917 he moved to the Jan Kazimierz University in Lviv and took up the independent position of professor of Polish language there, but in 1920 he returned to the Jagiellonian University to take over the position of professor of Slavic philology abandoned by Jan Łoś, and after the death of Łoś in 1928 also the chair of Polish language.

He was an expert of the Polish delegation at the Paris peace conference in 1919, dealing with geographic and ethnographic issues.

On November 6, 1939, he was arrested as part of the Sonderaktion Krakau operation, imprisoned in Sachsenhausen, from where he was released in February 1940.

Kazimierz's cousin was Roman Nitsch, a microbiologist, a member of the Polish Academy of Arts and Sciences.