Lynch was born in the port of Valparaíso, Chile, the son of Estanislao Lynch y Roo, a wealthy Argentinian merchant resident in Chile who was a descendant of Patrick Lynch, and of Carmen Solo de Zaldívar y Rivera. His father, a former Colonel in the Army of the Andes, had settled in Chile from Argentina and was a grandson of Patrick Lynch, an emigrant from Galway to Buenos Aires in the 1740s. His connection to Patrick Lynch makes him a distant relative of Che Guevara.