Jaczewski was born in St. Petersburg, the son of geologist Leonard (1858—1916) and Helena née Biron.
After attending a German classical gymnasium he studied at the Saint Petersburg State University.
In December he joined an expedition to Brazil led by Tadeusz Chrostowski.
He received a doctorate from the University of Poznan in 1925 and taught geography in schools in Warsaw until 1935.
[1] He published many papers on the insect fauna of Poland and with I.M Kerzhner 1964 wrote Order Hemiptera (Heteroptera).