The House of Lords held that the manufacturer owed a duty of care to her, which was breached because it was reasonably foreseeable that failure to ensure the product's safety would lead to harm to consumers.

This was an evolutionary step in the common law for tort and delict, moving from strict liability based upon direct physical contact to a fault-based system that only required injury.

[6]: 4  The owner of the café, Francis Minghella,[Note 3] brought over a tumbler of ice cream and poured ginger beer on it from a brown and opaque bottle labelled "D. Stevenson, Glen Lane, Paisley".

[3][8] According to her later statements of facts, she was required to consult a doctor on 29 August and was admitted to Glasgow Royal Infirmary for "emergency treatment" on 16 September.

[6]: 11 Donoghue subsequently contacted and instructed Walter Leechman, a local solicitor and city councillor whose firm had acted for the claimants in a factually similar case, Mullen v AG Barr & Co Ltd,[10] less than three weeks earlier[3] (see also George v Skivington).

[6]: 22 [12] The full allegations made by Donoghue were presented in five condescendences, which claimed that Stevenson had a duty of care to Donoghue to ensure that snails did not get into his bottles of ginger beer, but that he had breached this duty by failing to provide a system to clean bottles effectively, a system that would usually be used in the business and was necessary given that the ginger beer was intended for human consumption.

[9]: 7 Stevenson responded to the condescendences by denying that any of his bottles of ginger beer had contained snails and "that the alleged injuries are grossly exaggerated ... any illness suffered by the [claimant] was due to the bad condition of her own health at the time".

[9]: 6–7  In response to the writ, Stevenson pleaded four main arguments: Injuries resulting from defective products were normally claimed on the basis of a contract of sale between the seller and the consumer.

[3][6]: 17–18 Only Lord Hunter dissented, finding that negligence to be inferred and that the fact that the bottle contents could not be examined (because of the dark glass) gave rise to a specific duty of care that would allow consumers to claim for damages.

[6]: 18–19 However, neither of the circumstances in which negligence could be found in product liability cases applied to Donoghue: ginger beer is not intrinsically dangerous, nor did Stevenson intentionally misrepresent the threat it posed.

[3] This claim was supported by the minister and two elders of her church and meant that Donoghue was not required to provide security for costs in case she lost the appeal.

[6]: 40–41 At present I content myself with pointing out that in English law there must be, and is, some general conception of relations giving rise to a duty of care, of which the particular cases found in the books are but instances.

The liability for negligence, whether you style it such or treat it as in other systems as a species of "culpa", is no doubt based upon a general public sentiment of moral wrongdoing for which the offender must pay.

[11]: 44 He supported this broad test by citing Heaven v Pender[19] and rejected the cases in favour of a narrower interpretation of a duty of care with the example of negligently poisoned food, for which there had been no claim against the manufacturer.

[6]: 41 [11]: 44–46  He went on to suggest that there should be a duty of care owed by all manufacturers of "articles of common household use", listing medicine, soap and cleaning products as examples.

[6]: 51 [11]: 59–60 Lord Thankerton further argued that it was impossible "to catalogue finally, amid the ever-varying types of human relationships, those relationships in which a duty to exercise care arises apart from contract" and commented that he "should be sorry to think that the meticulous care of the manufacturer to exclude interference or inspection by the [seller] should relieve the [seller] of any responsibility to the consumer without any corresponding assumption of duty by the manufacturer".

He therefore found that Donoghue had a cause of action and commented that he was "happy to think that in ... relation to the practical problem of everyday life which this appeal presents ... the principles of [English and Scots law] are sufficiently consonant with justice and common sense to admit of the claim which the appellant seeks to establish.

[11]: 35  He held that there were only the two recognised exceptions to the finding of a duty of care and supported Baron Alderson's judgment in Winterbottom v Wright that "the only safe rule is to confine the right to recover to those who enter into the contract; if we go one step beyond that, there is no reason why we should not go fifty".

[6]: 44–46 In a case like the present, where the goods of the defenders are widely distributed throughout Scotland, it would seem little short of outrageous to make them responsible to members of the public for the condition of the contents of every bottle which issues from their works.

[6]: 50 [11]: 57–58  He further endorsed concerns that Lord Atkin's broader test of liability would have allowed everyone injured in the Versailles rail accident to be able to claim compensation from the manufacturer of the axle that broke and caused the crash.

"No amount of posthumous citation can of itself transfer with retrospective effect a proposition from the status of obiter dictum [passing comments] to that of ratio decidendi.

[25]: 8  Although she is listed on her death certificate as May McAllister, she was by then commonly known as Mabel Hannah, having adopted her mother's maiden name and the first name of her daughter, who had died when she was eleven days old.

[6]: 111  On 28 October 1931, just over one month before he heard Donoghue, Lord Atkin also used the principle in relation to defamation, perjury, fraud and negligence in a lecture at King's College London.

[34]: 22  However, Donoghue otherwise attracted little attention; it was understood only as precedent that manufacturers were liable for injuries their goods cause their ultimate consumers rather than that there was a general principle of liability in negligence.

[38]: 1027 In the sole dissenting judgment, Viscount Dilhorne held that the neighbour principle could not have been intended to be applied in all circumstances and that it could only be used to determine to whom a duty of care is owed rather than if one exists.

[38]: 1045  Chapman comments "that this conclusion appeared ... distinctly quaint, old-fashioned and even untenable in the light of [Donoghue] shows how far the law had moved in the four decades which separated the two House of Lords decisions".

[49] In 1996, retired Canadian judge Martin Taylor together with David Hay QC and Michael Doherty produced a documentary on the case: The Paisley Snail.

[50][51] In a speech scheduled to be delivered in May 1942 (although delayed by the Second World War), Lord Justice MacKinnon jokingly suggested that it had been proven that Donoghue did not find a snail in the bottle.

[6]: 170–171 This allegation, suggests Chapman, established itself as a legal myth;[6]: 172  it was repeated by Lord Justice Jenkins in a 1954 Court of Appeal practice note.

[52]: 1483  However, both MacKinnon and Jenkins were unaware that the trial had not gone ahead because of Stevenson's death, and the events following the case were only published in response to the practice note.