It is commonly agreed that the Channel Island Militias were formed in the 13th - 14th centuries. In 1337 Edward III ordered "all his faithful peoples of the islands" to be levied for war. There was, however, already a Militia in existence and compulsory service due to the constant threat of invasion from neighbouring France. The threat of invasion was ever present and various attempts were made throughout this period, there were two raids in 1338 and 1339. Later in the 15th century the east of Jersey was held by the French for seven years while the west of the Island was held by the Militia under de Carteret. Finally, the partial occupation ended when Harliston appeared with a fleet from England and the Militia crossed the island to besiege the French at Mont Orgueil Castle. This earned for the detachments of the Militia from St Ouen the honour of parading on the right of the Militia line.

Throughout this period there were various raids and invasion attempts by the French one of which occurred in 1549 when the French under Captain Francis Breuil (de Bretagne) landed with a fleet at Bouley Bay but were defeated during the bloody Battle of Jardin D'Olivet. It is believed that this is the first time the Jersey Militia fought in a Brigade Formation.

By 1622 the Jersey Militia consisted of three regiments, each under a Colonel, the West, North and East. During the English Civil War (1649-60) the majority of islanders were for the Parliamentarians but Elizabeth Castle and Mont Orgueil Castle were held for the Crown until George de Carteret won the island over to the Royal cause. He attacked the Parliamentarians by sea and Jersey became a thorn in their side. During the Civil War the Prince of Wales was protected in Elizabeth Castle while in Exile. After the Restoration in 1660 George de Carteret was granted land in the New World which he called New Jersey in recognition of his role during the Civil War and in gratitude for his support to the King.

1678 saw the re-modelling of the Jersey Militia when Sir Thomas Morgan was appointed the Governor of Jersey. He reviewed the Militia and the defences of the island, including the castles and forts. By 1685 the Militia consisted of three regiments and a troop of horse. Towards the end of this century the Channel Island Militias were receiving uniforms, arms and equipment from the British Government.

In 1730 there were five regiments made up of six battalions as follows:
1st - St Ouen, St Mary, St John
2nd - Trinity, St Martin
3rd - St Saviour, Grouville, St Clement
4th - 1st/4th St Helier 2nd/4th St Lawrence
5th - St Peter, St Brelade
By the code of 1771 there was compulsory service for all males between the ages of 17-35 and youths between 15-17 had to drill once a week. At this time there was one regiment of artillery, one of cavalry and six battalions of infantry in addition to the regular troops in the castles.

It was thanks to the regular troops and Major Francis Peirson that the French were defeated in the famous Battle of Jersey in 1781 with the support of the Jersey Militia. In 1781 the 95th Regiment (Derbyshire) were stationed in Jersey along with five companies of the 78th Regiment (Highland) and 83rd Regiment (Dublin). At 11.00pm on 5th January 1781 Baron de Rullecourt on a moonless night prepared to land at La Rocque in the east of the island guided by a local traitor. By 4-5 am they stepped ashore at La Platte Rocque and marched toward St Helier. They arrived in St Helier unobserved until Pierre Arrive came out of his house in Colomberie and was bayoneted to death. On reaching the Market Place (now the Royal Square) they killed a sentry at Picquet House but another escaped to raise the alarm at the General Hospital where the 78th Regiment were stationed. The Lieutenant Governor Moise Corbet was surprised in bed where he was captured and taken to the Court House where he was forced to sign the surrender, which ordered all arms to be delivered to the Court House.

De Rullecourt deployed his troops in the Market Place, read a proclamation and sent out the order for surrender. Captain Mulcaster of the Corps of Royal Engineers rode to Elizabeth castle and took command of the garrison there. He was joined shortly after by a company of the St Lawrence Militia and later by the order to surrender. Mulcaster refused, stating "I don't understand French". De Rullecourt incensed by this refusal to surrender marched to Elizabeth Castle where he was fired on by the castle cannon, the second shot of which wounded two men, one of whom was the Lieutenant of Grenadiers, whose leg was severed. This caused chaos in the French ranks, and De Rullecourt who by now was furious ordered Corbet to send a message to the castle ordering them to surrender. Once again Mulcaster refused and when told of the 10,000 French troops who were supposedly on their way replied "All the better, there will be more to kill". Due to the rising tide De Rullecourt was forced to withdraw to the Market Place where he observed the massing of British troops on Mont Patibulaire (now Westmount) overlooking the town. These troops consisted of the 78th Regiment, the St Lawrence, St Saviour, St Ouen, St Mary, South West and North Regiments of Militia and also the 95th Regiment with all the cannon they could muster. De Rullecourt, however, was still optimistic that he would be triumphant.

At 10.30am on 6th January 1781 the greater part of the Militia had assembled, St Martin had already attacked the French rearguard at Grouville and later assembled on the Town Hill in support of the main battle. Major Peirson advanced from Westmount to the Market Place and was met by a French Officer sent by De Rullecourt with the order to surrender, Peirson replied in French "Yes we will carry our arms to the Court House, but there will be a bayonet on the end of every musket". The troops continued to advance and as they neared the town centre they split into two columns. The first under Captain Lumsdaine of the 78th Regiment with the Militia of St Lawrence, St Ouen and St John, these arrived in Vine Street, where they were fired upon by the French using the cannon taken from the Town Church. Colonel Thomas Pipon of the South West Militia marched up Broad Street. Peirson led the second column up King Street with the 95th Regiment and the remainder of the Militia.

In the early stages of the battle, Major Peirson was fatally wounded by a French soldier but was swiftly avenged by a militiaman and Peirson's black servant named 'Pompey'. The battle raged fiercely with bullets whizzing everywhere for not only were the combatants in the Market Place firing, but they were supplemented by the St Martins militia firing down from the Town Hill (now Fort Regent). Bullet holes can still be seen in the walls of the Peirson Public House today.

During the battle De Rullecourt came out of the Court House with the Governor and was shot and wounded by soldiers from the 78th Regiment (he died from his wounds some six hours later) and the French surrendered immediately. The time was now 12.30pm and the battle had lasted just fifteen minutes. Over 400 prisoners were taken and guarded by the St Lawrence Militia, the officers were held in the Court House. The Prisoners were subsequently despatched to England. The losses were severe with 78 French killed and 80 wounded, 8 of whom died later in hospital. Of the regular British Troops 12 died and 36 were wounded and the local Militia had 4 dead and 29 wounded. This was the last battle fought on British soil and was commemorated by two paintings 'The Death of Major Francis Peirson' by John Singleton Copley (1784) and 'The Battle of Jersey' by E.F. Burney (1787). Also, at the Bi-Centenary of the Battle of Jersey in 1981 two commemorative dishes were issued.

On 6th January 1831 on the 50th Anniversary of the Battle of Jersey the entire Channel Island Militias were granted the 'Royal' prefix by King William IV. At this time all the Militia insignia was changed in accordance with the 'Royal' title, including uniforms which now had blue facings. In 1844 the Parish Arsenals were built and the cannon removed from the Parish Churches. In the mid 1860's a Troop of Horse existed, known as the Royal Jersey Militia Dragoons. They carried messages on horseback between the regiments and wore black leather helmets with a black horse-hair plume and red tunics. The Troop was disbanded sometime during the 1870's. Also at this time Rifle Companies existed these wore the 1861 'quilted' shako. They too were short-lived and were disbanded when the Militia was reorganised once again in 1877; there were now three infantry regiments with 500 NCO's and men, each under a Lieutenant-Colonel. These were as follows:

1st - made up of old St Lawrence and 5th (South)
2nd - made up of old 2nd (North) and 3rd (East)
3rd - made up of old St Helier and residents of St Lawrence (ex 4th)

By General Order of 1881 from Her Majesty Queen Victoria the Battle Honour 'Jersey 1781' was granted to the following Militia Regiments, 1st (West), 2nd (East) and 3rd (South).

The Militia was reorganised yet again in 1890 into two field artillery companies, four garrison artillery companies and three light infantry battalions, West, Town and East. In 1891 there was a mutiny by Militiamen of the St Ouen section as they were not allowed to parade in their lawful position on the right of the line as had been previously accorded them, this mutiny was not due to disloyalty but to injured pride. A contingent of the Royal Jersey Militia took part in the Empire Parade in London on the occasion of HM Queen Victoria's Diamond (60th) Jubilee on 22nd June 1897.

The Militia came under the Army Act in 1905 and at this time it consisted of the Royal Jersey Artillery with two field batteries and two garrison companies, a Corps of Militia Engineers, a Militia Medical Company and three battalions of Light Infantry.

The Militia was mobilised in 1914 at the outbreak of the First World War and on 2nd March 1915 the Jersey Overseas Contingent consisting of 6 Officers and 224 Other Ranks under Captain, later Lieutenant Colonel, Stocker proceeded overseas to serve with the 7th Battalion of the Royal Irish Rifles. During the First World War 6,292 Jerseymen served in HM Forces, 862 were killed in action or died of wounds. During the First World War the Militia also provided part of the guard for the German Prisoner of War camp at Blanches Banque, St Brelade, in Jersey. In 1918 at the end of the war the Jersey Militia was demobilised and was subsequently was granted the Battle Honour 'The Great War 1914-1918'.

On 24th December 1921 a new law was passed reducing the Militia to just one Regiment entitled 'The Royal Militia of the Island of Jersey'. In 1925 new colours were presented and the old ones laid up in the various Parish Churches. Compulsory service was ended in 1929 and the strength reduced to just 260 men, the cost was to be borne by the States of Jersey and not the British Government.

Upon the outbreak of the Second World War the Royal Militia of the Island of Jersey (RMIJ) was mobilised once more and assembled at the Town Arsenal (now Jersey Fire Station) and marched to Fort Regent, overlooking St Helier, which became their Headquarters. On 2nd June 1940 the British Government recalled all the regular troops from the Channel Islands and on 20th June Lieutenant-Colonel H.M. Vatcher MC upon receiving orders for the demilitarisation of the island informed the Lieutenant-Governor that he had been recalled and the island would be undefended. He therefore requested permission for the RMIJ to leave the island to fight overseas. Permission was granted and at 3.00pm on 21st June 1940 11 Officers and 193 Other Ranks left for England on the potato ship SS Hodder. The German Forces subsequently invaded the Channel Islands on 1st July 1940 where they remained in occupation for almost five years. The first Germans to arrive in Jersey were in an aircraft from Aufklarungsgruppe 123 a Luftwaffe Reconnaissance Squadron.

The RMIJ initially served as the 11th (Royal Militia Island of Jersey) Battalion of the Hampshire Regiment and although the 11th Battalion did not leave the UK many members of the original contingent served in various theatres of the war, including Africa, Italy, Holland and France. Of the original 193 men who left the island in 1940 ten were killed in action.

On 8th May 1945 the Royal Navy sent HMS Bulldog & Beagle to the Channel Islands as part of Operation Nestegg in order to accept the German surrender. On 9th May 1945 Force 135 (Channel Islands Liberation Force) led by Colonel William P.A. Robinson MC of the Royal Artillery and his Adjutant Captain Hugh Le Brocq (RMIJ) landed at the harbour. They advanced to the Pomme D'Or Hotel where the Jersey Harbour Master Captain H.G. Richmond raised the Union Jack ending the German occupation of Jersey.

On 14th February 1946 the War Office advised the Lieutenant-Governor that the 11th (RMIJ) Battalion of the Hampshire Regiment was being disbanded and as the National Service Act was not adopted in the Channel Islands the RMIJ ceased to exist. On 10th January 1954 the Regimental Colours were laid up in the Town Church.

In 1986 the British Government requested that Jersey should contribute towards the Defence Budget of the United Kingdom and after much deliberation the Field Squadron Royal Engineers (Royal Militia of the Island of Jersey) Territorial Army was formed in October 1988. The role of the Squadron was later changed from a Field Squadron to a RAF Harrier Force Support Squadron. In 1995 on the 50th Anniversary of the Liberation of Jersey the Squadron was granted the 'Privilege' by the States of Jersey this is the equivalent to granting the freedom of the city. The Royal Militia of the Island of Jersey Association meet regularly throughout the year and is supplemented by members of the Field Squadron ensuring that the Association will continue for many years to come. Thus, the Royal Jersey Militia in its various forms has had a long and varied history.