The plant pathogen Phytophthora infestans emerged in Europe in 1845, triggering the Irish potato famine and massive European potato crop losses that continued until effective fungicides were widely employed in the 20(th) century. Today the pathogen is ubiquitous, with more aggressive and virulent strains surfacing in recent decades. Recently, complete P. infestans mitogenome sequences from 19(th)-century herbarium specimens were shown to belong to a unique lineage (HERB-1) predicted to be rare or extinct in modern times. We report 44 additional P. infestans mitogenomes: four from 19(th)-century Europe, three from 1950s U.K. and 34 from modern populations across the New World. We use phylogenetic analyses to identify the HERB-1 lineage in modern populations from both Mexico and South America, and to demonstrate distinct mitochondrial haplotypes were present in 19(th)-century Europe, with this lineage initially diversifying 75 years before the first reports of potato late blight.