"[1] Harmon enlisted in the 3rd United States Colored Infantry Regiment when it was formed in August 1863, and was promoted to the rank of sergeant before the end of the year.
At the end of the Civil War, a portion of the Third Regiment, including Harmon, was stationed in Gainesville, Florida.
[2] In letters to the Philadelphia Christian Recorder (a publication of the African Methodist Episcopal Church), Harmon expressed his dissatisfaction over the position of African-Americans in the South.
In the first two years after the end of the Civil War control of southern states was returned to men who had supported the Confederacy, who instituted black codes that restricted the rights of African-Americans.
Harmon concentrated on improvements to the administration of government and generally avoided controversial proposals on social issues, for which he was criticized by more radical elements of the Republican Party.
Harmon remained well regarded in the Republican Party, and he was appointed chief clerk of the Florida House of Representatives in 1873.
Despite the loss of opportunity for African-Americans in politics and in appointed positions in state government, Harmon remained active in the Republican Party.
Political patronage positions in the Federal government for African-Americans in the South ended when Grover Cleveland became President in 1885.
The next year Harmon and Saunders opened a law office in Tallahassee specializing in government land claims.
Harmon avoided political office while the charge was pending, declining an attempt to nominate him for mayor of Gainesville.
In 1876, Harmon served as the head of a committee on education at an assembly of "colored men" of Florida held in Tallahassee.
That year, the school board in Leon County appointed Harmon as principal of the recently rebuilt Lincoln Academy in Tallahassee.
With the loss of Federal patronage positions in Florida after 1885, and facing difficulties resuming a legal career with local and state courts increasing hostile to African-Americans, Harmon opened a successful cabinetmaking and upholstery business in Tallahassee.
[15][16][17] Harmon married local resident Sophia Ligon in Gainesville in November 1865, shortly after being discharged from the army.