He was the son of Joel and Frances Yeardley, small dairy farmers at Orgreave, near Rotherham, Yorkshire. John was admitted a member of the Society of Friends in his twentieth year, entered a manufactory in Barnsley, and married, in 1809, Elizabeth Dunn, a convinced Friend much his senior. He commenced preaching in 1815, moving from place to place in the northern counties.
In 1821 Yeardley's wife died, and, led by a persistent "call," he decided to settle at Pyrmont in Germany, where a small body of Friends existed. For his subsistence he arranged to represent some merchants who imported linen yarn, and later on he commenced bleaching on his own account. His philanthropic labours included the establishing of schools and meetings for the young, and many notable persons, including the prince and princess of Prussia, came to hear him preach. In 1824 he accompanied Martha Savory, an English Quaker, on a gospel journey up the Rhine from Elberfeld to Würtemberg, Tübingen, and other German towns, through Switzerland to Congénies in Central France, where some Friends were and (as of 1897) still are settled. They visited Theodor Fliedner at Kaiserswerth, and all the principal religious and philanthropic institutions on their route.