On February 4, 1854 he was commissioned a Major or Binbashi in the army of the Ottoman Empire and soon advanced to the rank of Lieutenant Colonel or Kaymakam. He adopted the name of "Nessim Bey". Initially a staff officer Tevis led a force of Bashi-bazouks under General György Kmety in the Battle of Kurekdere, Battle of Indjédéré and the Siege of Kars. He was made an Officer in the Order of the Medjidie, a Grand Officer in the Order of Glory of the Ottoman Empire and was awarded the Medal for the Defence of Kars and the British Crimea Medal.