| Election Name: | 1866 New Hampshire gubernatorial election |
| Country: | New Hampshire |
| Type: | Presidential |
| Ongoing: | no |
| Previous Election: | 1865 New Hampshire gubernatorial election |
| Previous Year: | 1865 |
| Next Election: | 1867 New Hampshire gubernatorial election |
| Next Year: | 1867 |
| Election Date: | 13 March 1866 |
| Nominee1: | Frederick Smyth |
| Party1: | Republican Party (United States) |
| Popular Vote1: | 35,137 |
| Percentage1: | 53.53% |
| Nominee2: | John G. Sinclair |
| Party2: | Democratic Party (United States) |
| Popular Vote2: | 30,481 |
| Percentage2: | 46.44% |
| Map Size: | 245px |
| Governor | |
| Before Election: | Frederick Smyth |
| Before Party: | Republican Party (United States) |
| After Election: | Frederick Smyth |
| After Party: | Republican Party (United States) |
The 1866 New Hampshire gubernatorial election was held on 13 March 1866 in order to elect the Governor of New Hampshire. Incumbent Republican Governor Frederick Smyth won re-election against Democratic nominee John G. Sinclair.[1]
On election day, 13 March 1866, incumbent Republican Governor Frederick Smyth won re-election by a margin of 4,656 votes against his opponent Democratic nominee John G. Sinclair, thereby retaining Republican control over the office of Governor. Smyth was sworn in for his second term on 5 June 1866.[2]