Adelaide Helen Grant Sinclair, OC OBE (January 16, 1900 – November 20, 1982) was a Canadian public servant.

Born in Toronto, Ontario, the daughter of Dr. and Mrs. Overton Macdonald, she attended Havergal College and received a Bachelor of Arts degree in economics from University College, University of Toronto in 1922 and a Master of Arts in 1925.

During World War II, she was the Director and temporary Commander of the Women's Royal Canadian Naval Service (WRCNS).

She was made an Officer of the Order of the British Empire in the New Year Honours 1945 for her "untiring zeal and outstanding ability, tact and judgement in organizing the Women's Royal Canadian Naval Service into a most efficient and well-disciplined unit".

From 1946 to 1957, she was the executive assistant to the Deputy Minister of National Health and Welfare and Canadian representative to UNICEF.