During the latter part of the Greek War of Independence (1824-1827) he accompanied Ioannis Kapodistrias to Greece, and was appointed by him minister of war. When Kapodistrias was murdered in 1831 Metaxas became a member of the provisional government which held office till the accession of King Otto in 1833. During the minority of Otto he was named privy councillor and minister at Madrid and Lisbon.
In 1840 he was recalled and appointed minister of war. In 1843-1844 he was president of the council of ministers, and he subsequently held the post of ambassador at Constantinople from 1850 to 1854. He died in Athens in 1860.