“You better live your best and act your best and think your best today, for today is the sure preparation for tomorrow and all the other tomorrows that follow.”

Martineau wrote many books and a multitude of essays from a sociological, holistic, religious, domestic, and perhaps most controversially, feminine perspective; she also translated Auguste Comte’s Cours de philosophie positive as The Positive Philosophy of Auguste Comte, Freely Translated and Condensed, 2 vol. (1853). Martineau said of her own approach to writing: "when one studies a society, one must focus on all its aspects, including key political, religious, and social institutions". She believed a thorough societal analysis was necessary to understand women's status under men.

Martineau began losing her senses of taste and smell at a young age, becoming increasingly deaf and having to use an ear trumpet. It was the beginning of many health problems in her life.  In 1839, during a visit to Continental Europe, Martineau was diagnosed with a uterine tumour.  She moves to a house in Tyneside to be near her brother-in-law, Thomas Michael Greenhow, who was a celebrated doctor in Newcastle upon Tyne.  Immobile and confined to a couch, her illness caused her to literally enact the social constraints of women during this time. Whilst there she wrote three works including Life in the Sickroom, considered to be one of Martineau's most under-rated works. It upset evangelical readers as they "thought it dangerous in 'its supposition of self-reliance'".

In 1845 she left Tynemouth for Ambleside in the Lake District, here she designed herself and oversaw the construction of the house called The Knoll, Ambleside, where she spent the greater part of her later life.  Diagnosed with fatal heart disease in 1855, Martineau began her autobiography in 1855 (it was published posthumously in 1877), but she lived another 21 years, producing eight more volumes of serious work, and became England's leading woman of letters, holding a kind of court at her tiny estate in Westmoreland, where she died on June 27, 1876.

The subsequent works offered fictional tutorials on a range of political economists such as James Mill and Jeremy Bentham. Martineau relied on the works of Thomas Malthus to form her view of the tendency of human population to exceed its means of subsistence. However, in stories such as "Weal and Woe in Garvelock", she promoted the idea of population control through what Malthus referred to as "voluntary checks" such as voluntary chastity and delayed marriages. Historically she is remembered as a tough-minded writer who fought great odds to achieve a distinguished literary career.