Educated at the Lycée Condorcet, Ecole des Hautes Etudes, Ecole des Sciences Politiques, he had a brilliant career as a scholar, and was called to the Parisian bar, where he practised from 1881 to 1886, but eventually devoted himself to the study of numismatics. He became Chair in ancient numismatics at the Collège de France and was a director of various journals. In 1917, during World War I, he worked on assignment in the United States.
He wrote important works on the ancient kingdoms of Asia Minor–Trois royaumes de l"Asie Mineure, Cappadoce, Bithynie, Pont (1888), Mithridate Eupator (1890).
Also a critical edition and translation with H Weil of Plutarch"s Treatise on Music. And an Histoire des Israélites depuis la ruine de leur indépendance nationale jusqu"à nos jours (2nd ed, 1901).
From 1888 to 1897 Théodore Reinach edited the Revue des études grecques. He received an honorary Doctorate of Letters (Doctor of Letters ) from the University of Dublin in June 1902.
In 1886, Théodore Reinach married Charlotte Marie Evelyne Hirsch.
They had two daughters but she died at age twenty-six in 1889. Théodore Reinach married a second time in 1891 to Fanny Kann, a daughter of Maximilien Kann and Betty Ephrussi. They made their home in a chateau at Louisiana Motte-Servolex in the Savoie department in southeastern France.
The Reinachs spent time on the French Riviera and in 1902 hired the architect Emmanuel Pontremoli to design a villa at Beaulieu-sur-Mer.
Completed in 1908 the Greek-style property was named Villa Kerylos. Fanny Reinach died in 1917 and Theodore in 1928.
Théodore"s son, Léon (1893–1943), became the keeper of the archives at Villa Kerylos. Léon Reinach was married to Béatrice de Camondo with whom he had two children.
Today, the Villa Kerylos is a museum open to the public.
Inspired by the beauty of the Reinach"s Villa Grecque Kérylos and the area, nearby they built Villa Ephrussi de Rothschild.
Académie des Inscriptions et Belles-Lettres]
As a resident there, Théodore Reinach was elected to the Chamber of Deputies of France as a member of the Bloc des gauches, serving from 1906–1914. He was a member of the Institut de France and on his death he bequeathed the Villa Kerylos to the Institut. Fanny Reinach"s mother was a member of the Ephrussi family whose cousin Maurice was married to Béatrice de Rothschild.