In 1864, he graduated from Universität Dorpat with the degree of Doctor of Medicine for his dissertation about variations in body temperature in sick and healthy people (German: Experimentelle Beiträge zer Kenntniss der Wärmeregulirung beim Menschen).

From 1873 to 1890, he was a doctor at a school for deaf-mutes, and from 1881 to 1886 he taught internal medicine in medical courses for women.

From 1884 he was a consultant in internal medicine for the Office of the Institutions of Empress Maria (Russian: Ведомство учреждений императрицы Марии, romanized: Vedomstvo uchrezhdeniy imperatritsy Marii).

[1] In 1904, Kernig described acute pericarditis after severe attacks of angina pectoris and gave an explanation of its pathogenesis, forming part of the foundational research on myocardial infarction.

He was one of the principal organizers of higher women's medical education in Russia and provided initiative for the establishment of the Medical Institute for Women (Russian: Женский медицинский институт, romanized: Zhenskiy meditsinskiy institut).