Precisely when John Byset arrived with his family from Scotland is unknown, but he appears in the (surviving) English documents relating to Ireland in 1245, when Henry III of England orders 50 marks to be given out of the treasury to him as a gift.

It is possible that the Bissetts aided de Lacy against his Scottish rival Donnchad, Earl of Carrick and received some of the latter's lands for their assistance,[2] but while attractive no account of such a thing is preserved.

Following de Lacy's death, Brian Ua Néill rose to become the most powerful king in all the north of Ireland and in the 1250s was busy smashing the young earldom to pieces, killing many of the English (presumably Scots also) and destroying their castles,[3] and the Bissetts may have been among the sufferers.

Despite the decrees of Edward I of England, they were reportedly welcomed by the owner Sir Hugh Byset, usually presumed to be a son of the Mac Eoin, and at this time Rathlin Island belonged to the Lordship of the Glens.

It was also here that Robert Bruce may have begun planning to re-conquer Scotland, and later Sir Hugh's manor of Glenarm is where his brother Edward arrived after their victory in the Battle of Bannockburn.

However, Hugh Byset was among the most prominent magnates in the greater region because Aonghus Óg of Islay mentions him in a 1301 letter to Edward I as his compatriot, the pair "awaiting the royal commands.

"[7] MacDonald's personal loyalty in practice to the English king is uncertain, perhaps complicating the matter, but Byset's is much more clearly established, because he is recorded a number of times, from the late 1290s, in the Anglo-Norman documents, being commanded to fight against the English king's enemies in Scotland, most notably Robert Bruce, the treasury (Crown) paying Byset's expenses for mustering his forces and equipping fleets to go against the Scots, and also sending supplies.

[8] When Edward Bruce invaded Ireland in 1315, Hugh Byset and the heads of several other families, Norman and Gaelic, joined Sir Thomas de Mandeville in opposing him.

In fact where Bruce landed, Olderfleet Castle, was quite possibly owned by the Bissett family, but no account is preserved of what if anything this may, if true, have had to do with strategic decisions made by either side.

[13] In The Brus, John Barbour reports the Bissetts, presumably led by Sir Hugh, again with de Mandeville, Logan, the Savages, altogether with the de Clares, FitzGeralds, Butlers and others, in an alliance defeated by Bruce's army,[14] but the account is confused, location unspecified, and receives no support from the annals and other reliable sources, making it unlikely to have occurred as reported by the poet if such an encounter took place at all.

Whether anything was carried out is unknown, and in any event the collapse of the Earldom of Ulster less than two decades later in 1333 was the beginning of the end of direct English authority in the region for a long period, leaving the Bissetts surrounded by several increasingly influential Gaelic powers.

But since this is also the earliest known occurrence of the Gaelic lineage or princely style Mac Eoin, only a few decades after the arrival of the family in Ulster, the Bissetts have already culturally assimilated to a notable degree: AU1287.2: A host was led by Richard de Burgh namely by the Earl of Ulster (that is, the Red Earl) into Tir-Eogain, whereby he deposed Domnall, son of Brian Ua Neill and Niall Culanach O'Neill was made king by him.

It is unknown what role the Bissetts might have played in this, but half a century later in 1383 they are found probably allied with the O'Neills against the remnants of the earldom, which were led by the Savage family.

[19] That the Bissetts were now formally allied to the O'Neills may be supported by several notices in 1387 of the death of one Sabia O'Neill (Sadhbh inghen Aodha Uí Néill), wife of the Mac Eoin Bissett, in which she is praised as "the choice woman of the descendants of Niall of the Nine Hostages in her time" and "a lady that far surpassed all the ladies of the Clanna Neill, in all good parts requisite for the character of a noble matron".

In describing the Gaelic Captains in the beginning of the first document, the officials report that "... some callyth themselffes Kynges, some Kynges Peyres, in their langage, some Prynceis (Flatha), some Dukes, some Archedukes... and obeyeth to no other temperall person... and hath imperiall jurysdyction in his rome [realm]..."[26] Gaelic Ireland is described as a patchwork of various overkingdoms, petty kingdoms, and other territories with limited to no national overlordship, although some might be practised at the provincial level, for example by the O'Neills in the case of Ulster.

Mac Eoin of the Glens and many other Scots and a great number of the Clann Domnaill Galloclaech and of the Clann Sithig were killed there, and O Neill went away as a defeated man after the slaughter of his followers.Above is the final report of an activity of the Mac Eoin Bissett family in the Irish and English sources, and it is assumed that not long after, the MacDonnells, newly of Antrim and the former friends and allies of the Bissetts, somehow managed to dispossess them of the Lordship of the Glens.

This not always completely reliable compilation, being the work of biased Tyrconnell scholars, claims this was caused by the Mac Eoin's refusal to give up his fine steed to Conn O'Donnell after it has been requested.

In the opinion of W. F. T. Butler the MacDonnell claim was of doubtful legality,[32] while according to George Hill they did not establish a permanent (or any) presence in the Glens until Alexander Carragh in the early 16th century, who is noticed campaigning in the Irish annals in the 1520s.

In 1573, six years after O'Neill's death, Sorley Boy (re-)petitioned, and this time for "a portion of the Glynns claimed by him by inheritance from the M[B]issetts", with the government thinking it a good idea to grant because they could use him against the Irish who were still refusing to submit.

[35] However, he himself soon became involved in a major conflict with the English, and ended up settling in The Route, the old MacQuillan lordship to the west of the Glens, while a younger brother, Donnell Gorme MacDonnell, swore fealty to Elizabeth in 1584 for "so much of the Glynns in Ulster as were the lands of Myssett, otherwise Bissett", agreeing to pay what yearly rents the Lord Deputy Henry Sidney decided, this being 60 beeves (cattle).

But less than two years later, and shortly before Elizabeth and James VI of Scotland agreed in the 1586 Treaty of Berwick that the MacDonnells would finally have the right to stay in Ireland, the Lord Deputy granted the lordship, the yearly rents again being 60 beeves, to Angus MacDonnell of Dunnyveg, another relative of Sorley Boy, with all its castles and "Myssett alias Byssett's lands" save Olderfleet Castle (by this time of uncertain origin to the parties involved), this to become the property of the Queen.

[37] This same year Sir Henry Bagenal, in his Description and Present State of Ulster, describes the Glynns as they were understood then as being:[38] ... so called because it is [they are] full of rockie and woodie dalles [dales], it [they] stretchethe in lengthe 24 miles (on the one side beinge backed with a very steepe and bogie [boggy] mounteyne and on th' other parte with the sea) on whiche side there are many small creekes betwene rockes and thickets, where the Scottish gallies [galleys] do commonlie land; at either end are very narrowe entries and passages into this countrey, which lieth directlie opposite to Cantire in Scotland, from which it is 18 miles distant.The Glynns contain seven baronies, these being Larn, Park, Glenarm (the seat of the lordship), Redbaye, Lade, Cary, and Mowbray, with Rathlin Island counted as an additional half barony, and they were understood to be:[39] ... some tyme th' enheritance of the Baron Myssett, from whom it discended to a daughter who was married to one of the Clandonells in Scotland, by whom the Scotts now make their clayme to the whole, and did quietlie possesse the same for many yeares, till now of late (beinge spoyled of their goodes), they were totalie banished into Scotland...Uncertain is whether Irish and English attempts to drive out the MacDonnells in the 16th century are meant, or if their "quiet possession" of the territory refers to the period of over a century before this when the lordship or most of it remained in the possession of the Bissett family.

[40] What is unknown is whether the Bissetts ever recognised the nominal overlordship of the much more powerful Scottish dynasty still based in the Western Isles, a different species of submission from giving up their lordship itself.

In the 11th year of Elizabeth's reign an Act of Parliament officially vested the "Baron Bissett's land" in the Crown of England, and in 1617–8 the MacDonnells' claim to it as "heirs unto Bissett" remained of importance,[41] with the new Viscount Dunluce's pedigree even provided for the record:[42] ... Eoin More or Eoin the Great, whose mother was Margaret Stuard, daughter to Robert King of Scotland, and whose wife was Mary Bised that was heir of the seven troohes of Glinnes, whereof Rachroin was parcel.