He took part in the battles of Karytaina, Valtetsi, the capture of Tripolitsa, where he was wounded, Dervenakia, where he particularly distinguished, Nafplio, in an expeditions to Eastern Greece, in the siege of Patras and others.
For his actions, Grigoris Papaflessas proposed to the War ministry that he be promoted to the rank of Taxiarhis (Brigadier). On the April 15, 1823 the Executive branch of War promoted him, asking the approval of the National Assembly. 
On June 15, 1823, as Brigadier, he was ordered to impose order in various regions. Later he was promoted to the rank of Chiliarchos. The relative documents of his promotion have not been found, but on June 24, 1823 the Minister of Interior (Protocol # 1072) notified the National Assembly that Nikitas and Dimitrios Flessas were dispatched to the region of Pyrgos to pacify the infighting amongst the Greeks.
On May 20, 1825, Flessas joined his uncle, Grigoris Papaflessas, in the Battle of Maniaki against the Egyptians of Ibrahim Pasha. Uncle and nephew both fell after a heroic defence against a much superior force.
- ECHO of MESSINIA: 12-5-1966
- HM Pal. ' Athens 1857 p. of 315
- GNP ' Athens 1857 oel. 141