| Thomas Guest | |
| Office1: | Ontario MPP |
| Term Start1: | 1871 |
| Term End1: | 1874 |
| Predecessor1: | James Trow |
| Successor1: | John McNeill |
| Constituency1: | Perth South |
| Party: | Conservative |
| Birth Date: | 27 October 1816 |
| Birth Place: | Ireland |
| Death Place: | St. Mary's, Ontario |
| Occupation: | Farmer |
Thomas Boy Guest was an Ontario political figure. He represented Perth South in the Legislative Assembly of Ontario from 1871 to 1874. He was born in Ireland in 1816.[1]
He served as reeve of St. Mary's in 1855 to 1856, warden for Perth County in 1856 and mayor of St. Mary's in 1864. He was also lieutenant-colonel of the local militia. He died at St. Mary's in 1884[2] and was buried at the St. Mary's Protestant Cemetery.[1]