He gained rapid promotion becoming in 1756 a Lieutenant Colonel in the Fifteenth Regiment of Foot. Impressed with his undoubted military acumen, William Pitt, the then Prime Minister, promoted Amherst in 1758 to the rank of Major-General and Commander-in-Chief of the British expedition charged with engaging and defeating the French armies in North America under the command of General Montcalm. His successes in what history was to call the Seven Years War were legion and remain commemorated to this day on an Obelisk that was erected in 1768 on the higher ground of Montreal Park, the name Amherst gave to his estate after his finest triumph, the capture of Montreal on 8th September 1760.

Amherst’s achievements were recognised on both sides of the Atlantic. He was made a Knight of the Order of the Bath in 1761 and at the same time lauded by the then Mayor of New York who proclaimed future generations of Americans ‘will not cease to Bless the name of Amherst’. This was to be sorely tested but a few years later when the colonists took up arms in the War of Independence against the Mother Country. For a short period Amherst became Governor of Virginia but he declined the command of the British Forces on the grounds that he ‘could not bring himself to fight against the Colonists to whom he had been so much obliged.’ This refusal earned him both the gratitude and respect of the American people and there are as a result today no fewer than three towns and colleges in New England alone named after Jeffery Amherst.

He served for 27 years from 1770 as Governor of Guernsey, essentially an honorary position. Made a Privy Councillor in 1772 he was elevated to the peerage on 20th May 1776 taking the title of Baron Amherst of Holmesdale Kent. He assumed the position of Commander-in-Chief of H.M. Land Forces in the years 1778-1782 and again in 1793-1795. He received his baton as Field Marshal in 1796 and died without issue in his eighty-first year on 3rd August 1797. The problem of a lack of heir on the continuation of the peerage had been ingeniously resolved in 1788 with the King ‘granting a Remainder’ to Jeffery’s nephew, William Pitt Amherst, and re-styling the Title Amherst of Montreal, Kent. On Jeffery’s death, the first barony expired but the second then devolved, according to the limitation of the patent, upon his nephew. Elevation to an Earldom came in 1826 and there were to be in total five Earls.

Jeffery was buried alongside the bodies of his two brothers, Admiral John Amherst and Lieutenant-General William Amherst, in the family vault in those days in the crypt of St Nicholas Church, Sevenoaks.

The inscription on the Obelisk is as follows:

To commemorate the providential and happy meeting of three brothers on this their Paternal ground on 25 January 1761 after a six years glorious war in which the three were successfully engaged in various climes, seasons and services.

Dedicated to that most able Statesman during whose Administration Cape Breton and Canada were conquered and from whose influence the British Arms derived a Degree of Lustre unparalleled in past ages.

Louisbour surrendered and Six French Battalions Prisoners of War 26 July 1758

Du Quesne taken possession of 24 November 1758

Niagara surrendered 25 July 1759

Ticondcroga taken possession of 26 July 1759

Crown Point taken possession of 4 August 1759

Quebec capitulated 18 September 1759

Fort Levi surrendered 25 August 1760

Ile au Noix abandoned 28 August 1760

Montreal surrendered and with it all Canada and 10 French Battalions layed down their Arms 8 September 1760

St Johns Newfoundland retaken 18 September 1762