Mary Theresa Hart studied at the National Academy of Design in New York and with Will Hicok Low[6] and Edgar Melville Ward.

The two sisters and their father commuted daily from Brooklyn to adjoining top-floor studios at 11 East 14th Street in Manhattan.

[7] Mary Theresa Hart often sat for portraits by her sister, offering an "intelligent grasp of the poses," and the two women occasionally collaborated on canvases.

[8] A poem about the artist trio ended in the refrain, "don’t you wish that you were smart, Like James, Letitia and Mary Hart?

Mary Theresa Hart exhibited (often alongside her sister, uncle, and father) at venues including the American Water Color Society, Art Institute of Chicago, Louisiana Purchase Exposition, New York Water Color Club, Pan-American Exposition, and National Academy of Design--a portrait of the two sisters, painted by both of them, won the National Academy's Norman W. Dodge $300 prize for Mary Theresa Hart in 1901.