| John Henry Harmanson | |
| Birth Date: | 15 January 1803 |
| Birth Place: | Norfolk, Virginia, U.S. |
| Death Place: | New Orleans, Louisiana, U.S. |
| Resting Place: | Moreau Plantation Cemetery, Pointe Coupee Parish, Louisiana |
| Nationality: | American |
| Education: | Jefferson College (Mississippi) |
| Occupation: | Politician, Lawyer |
| Party: | Democratic |
| Office: | Member of the United States House of Representatives from Louisiana's 3rd district |
| Term Start: | March 4, 1845 |
| Term End: | October 24, 1850 |
| Predecessor: | John Bennett Dawson |
| Successor: | Alexander Gordon Penn |
| Office1: | Member of the Louisiana State Senate |
John Henry Harmanson (January 15, 1803 – October 24, 1850) was a U.S. Representative from Louisiana.
Born in Norfolk, Virginia, Harmanson pursued classical studies and was graduated from Jefferson College, Washington, Mississippi.He moved to Avoyelles Parish, Louisiana, in 1830 and engaged in agricultural pursuits.He studied law.He was admitted to the bar and practiced.He served as member of the State senate in 1844.
Harmanson was elected as a Democrat to the Twenty-ninth, Thirtieth, and Thirty-first Congresses and served from March 4, 1845, until his death in New Orleans, Louisiana, October 24, 1850.He served as chairman of the Committee on Expenditures in the Post Office Department (Twenty-ninth Congress).He was interred in Moreau Plantation Cemetery, Pointe Coupee Parish, Louisiana.