Lagarde was born in Paris, France, into a family of academics. Her Father, Robert Lallouette, was a Professor of English; her mother, Nicole (Carré), was a Latin, Greek and French literature Teacher. Lagarde and her three brothers, all younger, spent their childhood in Le Havre where she attended the Lycée François 1er and Lycée Claude Monet. As a teenager, Lagarde was a member of the French national synchronised swimming team. After her baccalauréat in 1973, she went on an American Field Service scholarship to the Holton-Arms School for girls in Bethesda, Maryland. During her year in America, Lagarde worked as an intern at the United States Capitol, as Representative william Cohen's congressional assistant, helping him correspond with his French-speaking constituents during the Watergate hearings. She graduated from Paris West University Nanterre La Défense, where she obtained Master's degrees in English, labor law, and social law. She also holds a master's degree from the Institut d'études politiques d'Aix-en-Provence. Since 2010, she has presided over Sciences Po Aix's board of Directors. She also prepared for École nationale d'administration's entrance exam but ultimately failed to gain admission to the elite public administration school.