Mary Esther Miller MacGregor, (August 27, 1872 – February 10, 1961) also known as Marian Keith, was a Canadian author of fiction.

She contributed a column to Teacher’s Monthly and then worked on the editorial staff of the Presbyterian Church's Sunday School Publications.

[4] In many of her novels, MacGregor sought to portray her connection between religious thought and social conscience in order to improve life for the poor and uneducated.

[3] MacGregor authored more than a dozen novels and several biographies, including Courageous Women, which she co-authored with Lucy Maud Montgomery and Mabel Burns McKinley.

[5] Her ability to capture regional attitudes and her use of social anecdotes using a style characterized by zest and humour earned her a strong local following.