Windthorst was born at Kaldenhof manor in the present-day municipality of Ostercappeln, in the lands of the former Prince-Bishopric of Osnabrück, which had been secularised to the Electorate of Hanover under the Protestant Welf dynasty in 1803. The growth-restricted boy was raised in a Roman Catholic family, which for some generations had held important posts in the bishopric's civil service. Windthorst became a half-orphan at the age of ten, when his father died in 1822. He was educated at the Gymnasium Carolinum, an endowed school at Osnabrück which he left with excellent "Abitur" exams, and from 1830 studied law at the universities of Göttingen and Heidelberg. Influenced by the rise of liberalism during the "Vormärz" era and the 1832 Hambach Festival as well as by the Catholic theologian Georg Hermes, Windthorst tried to bring his Catholic confession in accordance with the ideals of liberty, civil rights and national unity.