Born Katherine Hayes, at Dalhousie, New Brunswick, she was a teacher, librarian, journalist and author. She also wrote poetry and composed songs and until marring C. Bowman Simpson in 1882 taught at various schools in the Maritimes. From 1891 to 1898 Simpson Hayes served as the first librarian for the Legislature of the Northwest Territories.
As a journalist she wrote for the Manitoba Free Press (1900-1906), Winnipeg Tribune and the Regina Leader Post (becoming its first female reporter), using the pen name Mary Markwell. In 1904 she was one of 16 women journalists who, while travelling via Canadian Pacific Railway to the St. Louis World Fair, founded the Canadian Women’s Press Club.
Simpson Hayes served as club president in 1906-1907. In 1907 she was sent overseas as publicity writer for the CPR and also served as an immigration commissioner. Her several books include Derby Days in the Yukon (1910) which she wrote using the pen name Yukon Bill; and a collection of poems, short stories and plays called Prairie Pot-Pourri (1915). The latter is considered to be the first book written and published in the Northwest Territories. She was still contributing to newspapers until a few years before she died of a heart attack in 1945 in Victoria, B.C.