Malvy entered the Chamber of Deputies in 1906 as a Radical; thereafter he served as under secretary under Ernest Monis (1911) and Joseph Caillaux (1911–12) and became minister of commerce under Gaston Doumergue (1913–14) and then minister of the interior under René Viviani. When World War I broke out, he remained minister under Aristide Briand and Alexandre Ribot (1915–17); but on July 22, 1917, Premier Georges Clemenceau charged Malvy with lax administration in dealing with defeatists and pacifists. Malvy resigned on August 31, and the Ribot cabinet fell. In October the royalist Léon Daudet accused Malvy of high treason. At Malvy's request, he was tried on both charges by the Senate, sitting as a high court; on Aug. 6, 1918, he was acquitted of the charge of high treason but was found guilty of forfaiture (culpable negligence in the performance of his duties) and sentenced to banishment for five years. He spent his exile in Spain.

Pardoned and returned to the Chamber of Deputies in 1924, Malvy remained active in politics until his retirement in 1940.