Lars Magnus was born in Värmskog, Värmland, and grew up in the small village of Vegerbol located between Karlstad and Arvika.

At the age of 12, Ericsson's father died forcing him to seek work as a miner.

He then worked for six years for an instrument maker named Öllers & Co. who mainly created telegraph equipment.

Upon his return to Sweden in 1876, he founded a small mechanical workshop together with his friend Carl Johan Andersson who had also worked at Öllers & Co..

When their daughter Anna was only six weeks old, their eldest son Johan died from pulmonary oedema.