[6][7] With an ongoing situation of war with Mexico brewing, Tevis was appointed at large to the United States Military Academy at West Point on June 30, 1845.

He converted to Roman Catholicism in 1853 where he received Baptism in the Chapel of the Archbishop of Paris, from the hands of then Monsignor Georges Darboy who was charged with Tevis's instruction and preparation in the faith.

[14] 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.

[6] In addition to organising the regiment and serving with them at the defence of Baltimore he was involved in operations around Gloucester Point, Virginia.

[26][27] The state of Maryland in the American Civil War contained large amounts of citizens loyal to both the Federal and Confederate governments.

In addition to normal wartime military operations Tevis's regiment patrolled the areas of elections and made arrests.

[28] Tevis entered the forbidden zone of politics when on November 2, 1863, he issued a proclamation not only declaring that all qualified voters should engage in their right to vote, but to vote for the platform of the Unconditional Union Party as "recognized by the Federal authorities as loyal or worthy of the support of any one who desires the peace and restoration of the Union".

[34] Brigadier General Thomas William Sweeny was made Secretary of War in late 1865 by the Fenian Brotherhood[35] who had a scheme to gain the independence of Ireland through military attacks on Canada.

[37] Though there are theories that the United States Government did not want the Fenian plans to actually succeed, Tevis was in the pay of the British Crown as a secret agent for £100 each month.

The British Ambassador to the United States Frederick Wright-Bruce reported that Tevis "quarreled with the Fenian leaders and is now ready to do them as much harm as possible".

For his efforts the Pope knighted Tevis Chamberlain of the Sword and Cape on February 22, 1868, and ennobled him with the title of Count.

General Stone, or "Ferik Pasha", recruited several American veterans of varying ranks who served with both the Federal Government and the Confederacy including Tevis.

[58] He was one of about fifty Americans who served in the Egyptian Army during the era of Khedive Ismail; relative to the others, his stint in Egypt was one of the shortest.

For the latter he resided in Bucharest during the Romanian War of Independence from April to November 1877[60] where he wrote an account of the Siege of Plevna.

[63] Whilst residing in Paris Tevis provided information to Great Britain acting as a double agent on plots by both Fenians[42] and Maharaja Duleep Singh, who proclaimed himself "the Sovereign of the Sikh nation and Implacable Foe of the British Government" [64] in a plot for a Sikh Uprising in India using Russian assistance.

[68] George Augustus Henry Sala's 1856 short stories The Dalgetty Race published in Household Words edited by Charles Dickens and A Journey Due North : Being Notes of a Residence in Russia[69] feature an American soldier of fortune "Nessim Bey" under the name "Washington Lafayette Bowie".