As a temporary brigadier-general,[1] he was responsible for the Jallianwala Bagh massacre that took place on 13 April 1919 in Amritsar (in the province of Punjab).

[4] After the massacre, he served in the Third Anglo-Afghan war, where he lifted the siege at Thal and inflicted heavy casualties on Afghans.

He was widely condemned for spearheading the Jallianwala Bagh massacre, both in Britain and India, but he became a celebrated hero among some with connections to the British Raj.

He was the son of Edward Dyer, a brewer of English heritage who managed the Murree Brewery, and Mary Passmore.

[14] Following his graduation, Dyer was commissioned into the Queen's Royal Regiment (West Surrey) as a lieutenant,[15] and performed riot control duties in Belfast (1886) and served in the Third Burmese War (1886–87).

Dyer served in the latter in the Black Mountain campaign (1888), the Chitral Relief (1895) (promoted to captain in November 1896)[18] and, after attending the Staff College, Camberley from 1896 to 1897,[19] the Mahsud blockade (1901–02).

[22] During the First World War (1914–18), he commanded the Seistan Force, for which he was mentioned in dispatches[23] and made a Companion of the Order of the Bath (CB).

A nationwide hartal (strike action), which was called on 30 March (later changed to 6 April) by Mahatma Gandhi, had turned violent in some areas.

The date coincided with that of the annual Baisakhi celebrations which are both a religious and a cultural festival of the Punjabis, and would have attracted visitors from outside the city.

On the morning of 13 April, Dyer issued a proclamation in English, Urdu and Punjabi at 19 locations around the city, and had handbills distributed, to the effect that a curfew was imposed, no processions were to take place, and that meetings of more than four individuals could be fired upon.

The proposed meeting was to take place in the Jallianwala Bagh, in defiance of the proclamation; Dyer saw this as an opportunity to, in his view, suppress rebels, and, as he claimed, do so in isolation from the general populace.

[37] The meeting assembled at Jallianwala Bagh, a walled space of 6 to 7 acres (2 to 3 ha) with five entrances, four of which were narrow, admitting only a few people at a time.

There were 3 or 4 small outlets in all and bullets were actually rained over the people at all these gates ... and many got trampled under the feet of the rushing crowds and thus lost their lives ... even those who lay flat on the ground were fired upon.

[45]The Hunter Commission report on the incident, published the following year by the Government of India, criticised both Dyer, and the Government of the Punjab for failing to compile a casualty count, so quoted a figure offered by the Sewa Samati (A Social Services Society) of 379 identified dead, comprising 337 men, 41 boys and a six-week-old baby,[4] with approximately 1,100 wounded, of which 192 were seriously injured.

[46] However other estimates,[47] from government civil servants in the city (commissioned by the Punjab Sub-committee of Indian National Congress),[48] as well as counts from the Home Political,[47] cite numbers of well over a thousand dead.

Made to the delegation in Urdu, the English translation of a segment of Dyer's statement is shown below, as given in Collett's The Butcher of Amritsar:[50] You people know well that I am a soldier and a military man.

If you wish for a war, the Government is prepared for it, and if you want peace, then obey my orders and open all your shops; else I will shoot.

Dyer devised what even one of his generally supportive superiors, O'Dwyer, described as an "irregular and improper" retaliation for the attack on Marcella Sherwood, designed, it seemed, to fall indiscriminately and humiliatingly on the local population.

Anyone wishing to proceed into the street between 6 am and 8 pm was made to crawl the 200 yards (180 m) on all fours, lying flat on their bellies.

"[56] The Morning Post claimed Dyer was "the man who saved India" and started a benefit fund which raised over £26,000 sterling.

In 1938, Gandhi wrote: "General Dyer himself surely believed that English men and women were in danger of losing their lives if he did not take the measures he did.

But strangers who do not accept the sacredness of the cow will hold it to be preposterous to kill a human being for the sake of slaying an animal (sic).

[79] In 1920, the British Labour Party Conference at Scarborough unanimously passed a resolution denouncing the Amritsar massacre as a "cruel and barbarous action" of British officers in Punjab, and called for their trial, the recall of Michael O'Dwyer and the Viceroy, Lord Chelmsford, and the repealing of repressive legislation.

As well as being "dazed and shaken up" – hardly the response of a soldier who had had murder in his mind – all the witnesses recall how Dyer "was unnerved and deeply upset about what had happened".

"[85][86] Collett quotes Dyer on the motivations that drove him to act as he did:[87] "It was no longer a question of merely dispersing the crowd but one of producing a sufficient moral effect, from a military point of view, not only on those who were present but more specially throughout the Punjab.

While he may have believed the Raj was threatened, and may have thought the mob was out to attack him and his soldiers, this does not justify his cavalier abuse of procedure and his indifference to Indian suffering.

He was presented with a gift of £26,000 sterling, (equivalent to £1,319,142 in 2023), which emerged from the fund raised on his behalf by The Morning Post, a conservative, pro-imperialist newspaper which later merged with The Daily Telegraph.

[92] Many Indians, including Nobel Laureate Rabindranath Tagore, were outraged by the fund for Dyer, particularly due to the families of the victims killed at the Jallianwala Bagh, who were still fighting for government compensation.

[2] The Conservative-leaning Morning Post defended him in an article titled "The Man Who Saved India", where they wrote that Dyer "did his duty, regardless of consequences".

"[99] Although still owning property in Wiltshire, Dyer died at his cottage in Somerset, St Martin's, Long Ashton, near Bristol.