Onisim Egorovich Kler was born in the commune of Corsel, located in the canton of Neuchâtel, to a family of civil servants. In 1862, he graduated from the Neuchâtel Industrial School in Switzerland. That same year, due to family circumstances that prevented him from entering university in his homeland, he moved to the Russian Empire.

Kler took a position as a governor for the princes Trubetskoy and successfully passed exams at the Imperial St. Petersburg University, gaining the right to teach French in educational institutions.

For about three years, he taught French in Moscow, then worked for about two years in Yaroslavl, where he actively participated in the activities of the local natural science society.

In 1867, Kler moved to Yekaterinburg, where a boys' gymnasium had been opened in 1861, and he took a vacant position as a French language teacher. He taught at the boys' gymnasium and the real school.

Kler showed interest in the nature and landmarks of the Yekaterinburg region. He was supported in this by the new director of the gymnasium V. V. Vsevolodov, the manager of the Mining School N. K. Chupin, and other colleagues. Soon, he proposed to create a "society of lovers of natural science" in the Urals, and this idea was supported.

Thus, at the initiative of the gymnasium teachers, the "Ural Society of Lovers of Natural Science" (USLNS) and a local history museum were established.

Kler became the curator of the museum and president of the USLNS, publishing about 60 works on local history.

Until his death in 1920, Onisim Egorovich remained the unchanging secretary and then president of the USLNS. He died suddenly of typhus on January 18, 1920, and was buried in the Lutheran-Catholic cemetery of Yekaterinburg, but his grave has been lost.