On 17 March 1773, Edgeworth's first wife Anna Maria Elers gave birth to their fifth child, Anna Maria Edgeworth, at the age of 29. Ten days later she died from puerperal fever. Edgeworth was still in Lyon to avoid temptation leaving his expectant wife in the care of Day. On learning of the death of his wife, Edgeworth travelled to London, where he consulted Day as to Honora Sneyd's situation. On learning that she remained in good health and unattached, he promptly headed to Lichfield to see Honora at the Sneyds, with the intention of proposing. His offer was accepted immediately, and there was no mention of the conventional waiting period before remarrying after widowhood. Although Mr. Sneyd was opposed to his daughter's marriage, the couple were married at Lichfield Cathedral on 17 July 1773, officiated by Canon Thomas Seward, Anna Seward being a bridesmaid. After marrying, problems with the Edgeworth family estates in Ireland required the couple to immediately move to Edgeworthstown, County Longford in Ireland.

Through this marriage Sneyd became step-mother to Edgeworth's four surviving children by his first wife, Anna Maria, ranging from seven months to nine years in age; Richard, Maria, who became a writer in her own right, Emmeline and Anna Maria. On encountering her new family she observed that Maria, then aged five, was exhibiting behavioural problems, and expressed her views that speedy and consistent punishment were the keys to ensuring good behaviour in children, a view she proceeded to practice. However, she believed that such discipline needed to be imposed "before the age of 5 or 6", and was therefore rather late in the case of the older children; however, she imposed a strict discipline. Following a period of ill health on Sneyd's part, Maria Edgeworth was sent away to boarding school in Derby (1775–1781), and later London upon the death of Honora Sneyd (1781–1782). Similarly, her older brother Richard was sent to Charterhouse (1776–1778) and then went to sea, and she never saw him again. Later Richard Edgeworth would comment on how difficult the first two years were for Sneyd in her new role as stepmother to undisciplined children, a role her relatives had advised her against.

Honora Sneyd was soon pregnant, giving birth to her daughter Honora on 30 May 1774, who died at the age of sixteen. Her second child, Lovell, who inherited the property, was born the following year on 30 June 1775. The Edgeworth children were raised according to the system of Rousseau, as refined and modified by the Edgeworths. Richard Edgeworth considered his early educational efforts a failure, the older children from his first marriage growing up unruly and then being sent away to school, and readily concurred with his new wife's stricter rules. However, he had seen very little of them in their early years.

After three years in Ireland, in 1776 they moved to England again, taking up residence in Northchurch,Hertfordshire Despite Anna Seward's despair at the loss of her friend, she and Honora had maintained regular correspondence and visits. However, these suddenly ceased, an event that Anna blamed Honora Sneyd's father for. During a temporary absence of Edgeworth on business in Ireland in the spring of 1779, Honora Sneyd fell ill with a fever, just as he was summoning her to let the house and join him there. On his return they consulted Erasmus Darwin at Lichfield, who was of the opinion the illness was more severe than at first thought, being a recurrence of consumption (T.B.) from which she had had a brief bout at the age of fifteen. He advised against returning to Ireland but rather, moving closer to Lichfield. For a while they stayed at the Sneyd house that was temporarily vacant while consulting a wide range of physicians including William Heberden (Samuel Johnson's physician), and even staying with Day near London to be close to medical care. but only received news of incurability. Eventually they rented Bighterton, near Shifnal, Shropshire, closer to the Sneyds, Darwin and others of their circle, where Honora Sneyd drew up her will in April.

Four years after returning to England Honora Sneyd died of consumption at six in the morning on 1 May 1780 at Bighterton, surrounded by her husband, her youngest sister, Charlotte and a servant. Honora Sneyd was buried in the nearby Weston church where a plaque on the wall (see box) bears witness to her life. Honora Sneyd died within eight years of her marriage to Richard Edgeworth, at almost the same age as her predecessor. The same disease which had taken the life of her mother and five maternal aunts would soon claim the life of her young daughter, Honora Edgeworth (1790), as well as her younger sister, Elizabeth, seven years later (1797), as well as at least two of Elizabeth's children, Charlotte (1807) and Henry (1813). Honora's brother, Lovell was also affected by the consumption. At the time it was thought this was a hereditary weakness carried by the family.

On Honora Sneyd's death, Edgeworth married her younger sister, Elizabeth Sneyd, stating that this had been the dying wish of Honora. Uglow speculates that this was a marriage of convenience, for the sake of the children. Although it was technically legal to marry one's wife's sister, the marriage was considered scandalous, and was opposed by the Sneyds, Sewards and Edgeworths as well as the Bishop. The couple fled to London where they were married on Christmas Day with Thomas Day as witness, before proceeding to live at Northchurch. The scandal may have given rise to less charitable interpretations of Edgeworth's actions, although there is no direct evidence to support or refute these. Honora Sneyd's will, drawn up during the last month of her life refers only to "that Woman whom he shall think worthy to call his, for her to wear, so long as they both shall LOVE", referring to a cameo she owned of Richard Edgeworth.

The Edgeworths jointly developed the concept of "Practical Education", a principle that would become a new paradigm by the 1820s. Having determined that after eight years, Richard Edgeworth's attempt to raise his eldest son Richard according to the principles of Rousseau was a failure, he and Honora were determined to find better methods. After the birth of Honora's first child (1774), the Edgeworths embarked on a plan, partly inspired by Anna Barbauld, to write a series of books for children. After trying many other methods, Barbauld's Lessons for Children from two to three years old was published in 1778, and the Edgeworths used it on Anna (5) and Honora (4), and were delighted to find that the girls learned to read in six weeks. Now back in England, at Northchurch the Edgeworths were in closer contact with the intellectuals of the Lunar society. Richard Edgeworth and Honora were determined to design a plan for the education of their children. They started by reviewing the existing literature on childhood education (including Locke, Hartley, Priestley in addition to Rousseau), and then proceeded to document their observations of the behaviour of children and then developed their own "practical" system. To this end Erasmus Darwin suggested they start by reading the work of Dugald Stewart. Honora Sneyd then started recording extensive notes on her observations of the Edgeworth children. These then became the dialogues in the final book.

Richard and Maria Edgeworth state that "She [Honora] was of opinion that the art of education should be considered as an experimental science", and that the failures of the past were due to "following theory rather than practice". Richard Edgeworth and Honora then set about applying the emerging principles of educational psychology to the actual practice of education. From their reading of theory they determined that the reason Barbauld was successful was that the child's reading was rewarded (thus departing radically from Rousseau), because it was associated with pleasure. Honora Sneyd conceived of the title of their work therefore as Practical Education. With her husband, Honora wrote the first version of Practical Education as a children's book Practical education: or, the history of Harry and Lucy for Honora her daughter, which was begun in 1778 and privately published in February 1780 in Lichfield as Practical Education, vol 2. The book tells a simple story of two parents and their two model children, Harry and Lucy, who carry out domestic chores and ask their parents many questions, the answers to which may be deemed educational. The children explain their discoveries and how they learn, the whole presented as nine forms of learning. As originally conceived it was intended to be the second part of a series of three books, but the remaining parts remained unwritten. The original plan had been for a collaborative work, contributed to by various members of the Lunar Society. it was an ambitious project designed to fill what they perceived of as major deficiencies in the field of both technical and scientific education and to introduce early ideas on morality, science and other academic disciplines into the developing mind of the young child. After Honora Sneyd's premature death, her sister Elizabeth continued the work, in her role as the third wife of Richard Edgeworth. The final version of the book was authored by Richard and Maria Edgeworth and published after both Honora and her sister Elizabeth's deaths, in 1798, and further revised under Maria's name as Early lessons (1801–1825). In reality this was a family project contributed to by a number of their members that would extend over 50 years, beyond Richard Edgeworth's death in 1817 (c. 1774–1825).

Richard Edgeworth observed on his wife's death that being familiar with the experimental method in science, she was surprised to find that educational theory was based on very little empirical evidence, and set out to apply experimental science to child education and devised, executed and recorded experiments with children. She conceived and executed a register (2 volumes 1778–1779) of the reaction of children to new knowledge and experience, given her interest in applying experimental science to the field of child education. She observed the questions that children asked, what they did, and how they solved problems. An extensive example of her recorded dialogue is given by Richard and Maria Edgeworth in "Practical Education". This formed the basis of Richard Edgeworth's Essays on professional education (1809). In the Bodleian Library there is a short story in manuscript dated 1787 and other fragments attributed to Honora Sneyd. Her parents' principles of childhood education were to be a profound influence on Maria Edgeworth's own career as a writer for children.

Honora Sneyd, through her early contact with members of the Lunar Society, had always taken a keen interest in science, an attribute that drew the intention of Richard Edgeworth who considered himself an inventor. Following their marriage, she worked on his projects with him and in his words, "became an excellent theoretic mechanick" herself.

Since little of Honora Sneyd's own words have survived, our image of her is largely through the eyes of others, in particular Anna Seward and Richard Edgeworth. Honora Sneyd is often listed amongst the members or associates of the Bluestockings, educated upper class literary women who disdained traditional female accomplishments and often formed close female friendships. The depiction of the effect of consumption on her has been used as a symbol of the pervasiveness of the disease in eighteenth-century culture. The work she started on educational psychology would prove to be immensely influential throughout the nineteenth century. Her name is also inextricably entwined with that of Anna Seward in the literature of lesbian relationships and female friendship.

From growing up in the Seward household with Canon Seward and the members of the Lunar Society, Honora Sneyd and her childhood friend Anna Seward developed relatively progressive views for the times on the status of women and equality in marriage, a key to which was female education. Sneyd entered into marriage with Richard Edgeworth on the understanding that they were equal partners in his work. Anna, and later Honora's stepdaughter, Maria Edgeworth, were to take those values and promote them in late-eighteenth- and early-nineteenth-century Britain, the ancestors of modern feminists. Today Honora's position on women's rights is best remembered for her rebuke of Thomas Day and his theory of the "perfect wife".

Anna Seward's will mentions two likenesses of Honora Sneyd in her possession that she wished to bequeath. The first of these was a mezzotinto engraving after George Romney, which she had modeled for as "Serena" (see Figure, above) to Honora's brother Edward. The other was a drawn miniature portrait by John André (1776) which she left to her cousin and confidante Mary Powys. A jasper medallion, after an image by John Flaxman, was issued by the Wedgwood factory in 1780 (right). Honora Sneyd was the subject of many of Seward's poems, When Sneyd married Edgeworth, she became the subject of Seward's anger, yet the latter continued to write about Sneyd and her affection for her long after her death. In addition to being immortalised in Anna Seward's poetry, Sneyd appears semi-fictionalised as a character in a play about Major André and herself, André; a Tragedy in Five Acts by William Dunlap, first produced in New York in 1798.

The plaque in St. Andrew's Church, Weston, where she is buried, on the north wall of the tower, reads;

• Parents

  Edward Sneyd (1711–1795) m. 1742 Susanna Cook d. 1757, by whom;

  Elizabeth Sneyd (1753–1797)

  Charlotte Sneyd d. 1822

• Foster family

  Thomas Seward (1708–1790) m. 1741 Elizabeth Hunter d.  1780, by whom;

  Anna Seward (1742–1809)

  Sarah Seward (1744–1764)

• Extended family

  Henry Powys d. 1774 m. Susannah Sneyd (1729–1791), by whom

  Mary Powys d. 1829

• Literary acquaintances

  David Garrick (1717–1779)

  Erasmus Darwin (1731–1802)

  Samuel Johnson (1709–1784)

  James Boswell (1740–1795)

• Suitors

  John André (1751–1780)

  Thomas Day (1748–1789)

• Husband and children

  Richard Lovell Edgeworth (1744–1817)

  m. 1763 (1) Anna Maria Elers (1743–1773), by whom;

  Richard Edgeworth (1765–1796)

  Lovell Edgeworth (1766–1766)

  Maria Edgeworth (1768–1849)

  Emmeline Edgeworth (1770–1817)

  Anna Maria Edgeworth (1773–1824)

  m. 1773 (2) Honora Sneyd (1751–1780), by whom

  Honora Edgeworth (1774–1790)

  Lovell Edgeworth (1775–1842)

• Influences

  Jean-Jacques Rousseau (1712–1778)

  Anna Barbauld (1743–1825)

  John Locke (1632–1704)

  David Hartley (1705–1757)

  Joseph Priestley (1733–1804)

  Dugald Stewart (1753–1828)

• Artists

  John Flaxman (1755–1826)

  James Hopwood (c. 1740–1819)

  George Romney (1734–1802)

• Other

  William Dunlap (1766–1839)

  William Heberden (1710–1801)

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