| Duncan Sinclair | |
| Birth Date: | 1869 1, df=yes |
| Birth Place: | Minto Township, Ontario |
| Spouse: | Martha A. McEachern m. 15 January 1894[1] |
| Riding: | Wellington North |
| Predecessor: | John Pritchard |
| Successor: | John Knox Blair |
| Term Start: | October 1925 |
| Term End: | May 1930 |
| Profession: | Salesman |
| Party: | Conservative |
Duncan Sinclair (29 January 1869 - 21 June 1951) was a Conservative member of the House of Commons of Canada. He was born in Minto Township, Ontario and became a salesman.
He was first elected to Parliament at the Wellington North riding in the 1925 general election, then re-elected there in 1926. Sinclair was defeated by John Knox Blair of the Liberals in the 1930 federal election. Sinclair made an unsuccessful bid to unseat Knox in the 1935 election.