He served as assistant city attorney of New Orleans from 1900 to 1910. During that same period, he was the District 14 member of the Louisiana House of Representatives for Orleans Parish. He was House Speaker from 1908 to 1910.[2] In 1908, he chaired the Louisiana Democratic State Convention.
Dupré was elected to the Sixty-first Congress to fill the vacancy caused by the death of Samuel Louis Gilmore. He was reelected to the Sixty-second and the six succeeding Congresses and served from November 8, 1910, until his death in Washington, D.C., on February 21, 1924. He is interred at the Catholic Cemetery in his native Opelousas.