John Alexander Dewar (February 7, 1863 – August 14, 1945) was a farmer and political figure on Prince Edward Island. He represented 3rd Kings in the Legislative Assembly of Prince Edward Island from 1912 to 1917 as a Conservative. Following several votes against his party in the 38th General Assembly, Dewar lost the Conservative nomination in his district. He ran and won re-election as an Independent the 1919 election, but was unable to win in 1923.^[1]

He was the son of Robert Dewar and Jessie Dewar. In 1908, he married Laura McPhee. Dewar was a director and vice-president of the provincial Dairyman's Association.

His brother George F. Dewar also served in the provincial assembly, as did his son Lloyd George Dewar.