| John Howard Sinclair | |
| Constituency Mp: | Antigonish—Guysborough |
| Parliament: | Canadian |
| Predecessor: | District was created in 1914 |
| Successor: | Colin Francis McIsaac |
| Term Start: | 1917 |
| Term End: | 1921 |
| Constituency Mp2: | Guysborough |
| Parliament2: | Canadian |
| Predecessor2: | Duncan Cameron Fraser |
| Successor2: | District was abolished in 1914 |
| Term Start2: | 1904 |
| Term End2: | 1917 |
| Office3: | Member of the Nova Scotia House of Assembly for Guysborough |
| Term Start3: | 1894 |
| Term End3: | 1904 |
| Birth Date: | 27 May 1848 |
| Birth Place: | Goshen, Nova Scotia |
| Party: | Liberal |
John Howard Sinclair (May 27, 1848 - June 8, 1924) was a Canadian politician.
Born in Goshen, Guysborough, Nova Scotia, Sinclair was educated in the Common School of Goshen, Guysborough Academy and Dalhousie College, Halifax. A lawyer, he was Mayor of New Glasgow in 1890-91 and member of the Nova Scotia House of Assembly from 1894 to 1904. He was elected to the House of Commons of Canada for Guysborough in a 1904 by-election after the sitting MP, Duncan Cameron Fraser, was appointed a Judge of the Nova Scotia Supreme Court. A Liberal, he was re-elected in 1904, 1908, 1911, and 1917.