Loudon was born in Cambuslang, Lanarkshire, Scotland to a respectable farmer. Therefore, as he was growing up, he developed a practical knowledge of plants and farming. As a young man, Loudon studied biology, botany and agriculture at the University of Edinburgh. When working on the layout of farms in South Scotland, he described himself as a landscape planner. This was a time when open field land was being converted from run rig with 'ferm touns' to the landscape of enclosure, which now dominates British agriculture.