Lamont, whose father worked in the customs service, came from an old but impoverished family in Braemar, Scotland. After his father's death in 1816 the young Lamont was sent to the Scottish Benedictine monastery at Ratisbon and given a rigorous mathematical training from the abbot. He was admitted to the Munich Academy of Science in 1827 and became assistant astronomer at the Bogenhausen Observatory in 1828 and director in 1835. In 1852 he became professor of astronomy at Munich University.

Lamont published a major catalog in six volumes (1866–74) of 34,674 small stars but his most important work was on terrestrial magnetism. He began keeping local records in 1836 and performed magnetic surveys of Bavaria, France, Spain, Denmark, and North Germany. He announced the important discovery of the Earth's (approximately) ten-year magnetic cycle in 1850, only a few years after Heinrich Schwabe had announced a similar cycle for sunspots. It was not long before scientists began to speculate on a possible connection.