Bernard Phélan was an Irish wine broker who immigrated to Bordeaux at the end of the 18th century. After marrying a local French woman, Bernard purchased two vineyards in Saint-Estéphe. His son, Frank, took over upon Bernard's death in 1841 and the family continued making some of the best wines grown in the gravelly-alluvial soils of Saint-Estéphe.

Today, the estate is planted to 58% Cabernet Sauvignon, 39% Merlot with small amounts of Cabernet Franc and Petit Verdot. All grapes are harvested manually with lots of care at the optimum ripeness each vintage. The wines are fermented for roughly 12 days in tank and macerated afterwards for about 20 days to ensure proper extraction. After blending, Phélan Ségur is aged for around 12 months, with no more than 50% new French oak used. All barrels are racked and returned by hand.