Lewis Wilkieson Johnstone (10 April 1862 – 9 March 1936) was a Conservative member of the House of Commons of Canada.
He was born in Sydney, Nova Scotia and became a physician and surgeon.
He is the grandson of Edmund Murray Dodd (1797-1876), who represented Sydney, Nova Scotia in the Nova Scotia House of Assembly and served as a Judge in the Supreme Court of Nova Scotia.
He is also a descendant of David Mathews, the Loyalist Mayor of New York City under the British during the American Revolution.
He is a descendant of the Schuyler family.
Johnstone attended King's College at Windsor, Nova Scotia, then in 1886 graduated in medicine from Bellevue Hospital Medical College.
He became a municipal councillor and mayor of Sydney Mines.He was first elected to Parliament at the Cape Breton North—Victoria riding in the 1925 general election then re-elected there in 1926 and 1930.
Johnstone was defeated in the 1935 election by Daniel Alexander Cameron of the Liberal party.