Born in Kampos, on the Messenian side of the Mani Peninsula, he was the son of Spyridon-Galanis Koumoundouros, the bey of the area during the last period of the administration of the region by the Ottoman Empire.

Koumoundouros’ long career encompassed many facets of political life, including serving in parliament, authoring of legislation, promotion of a democratic regime, restoration of the army, distribution of national farms to landless farmers, and the approval of major construction work (such as the Isthmus of Corinth).

Despite often experiencing inimical conditions, including at least three assassination attempts, he still managed to create a firm foundation for democracy in Greece.

Koumoundouros’ greatest achievement came in 1881, during his last (tenth) premiership, when after the Congress of Berlin and after diplomatic contacts with the Ottomans, he managed to bring about the annexation of the areas of Thessaly and Arta to the Greek mainland (with the Convention of Constantinople).

After the end of the unsuccessful Cretan revolution, he married Ekaterìni Konstantinou G. Mavromichàli of the famed Maniot family.

Ekaterìni died young and Koumoundouros married Efthimìa Perotì who presented him with his second son in 1858, Spirìdonas and in 1867 a daughter, Olga.