Around 1350 Thomas Mortimer was born illegitimately to Roger Mortimer 2nd Earl March.
Before 1352 [his father] Roger Mortimer 2nd Earl March and Philippa Montagu Countess March were married. She by marriage Countess March. She the daughter of William Montagu 1st Earl Salisbury and Catherine Grandison Countess of Salisbury. He the son of [his grandfather] Edmund Mortimer and [his grandmother] Elizabeth Badlesmere Countess Northampton.
In 1354 [his father] Roger Mortimer 2nd Earl March was restored 2nd Earl March
On 26th February 1360 [his father] Roger Mortimer 2nd Earl March died. He was buried at Wigmore Abbey. [his half-brother] Edmund Mortimer 3rd Earl March, Earl of Ulster succeeded 3rd Earl March, 5th Baron Mortimer of Wigmore.
On 24th August 1369 [his half-brother] Edmund Mortimer 3rd Earl March, Earl of Ulster and [his sister-in-law] Philippa Plantagenet Countess March 2nd Countess Ulster were married at Reading Abbey, Berkshire. She by marriage Countess March. He by marriage Earl of Ulster. She the daughter of Lionel of Antwerp 1st Duke of Clarence and Elizabeth Burgh Duchess of Clarence. He the son of [his father] Roger Mortimer 2nd Earl March and Philippa Montagu Countess March.
On 27th December 1381 [his half-brother] Edmund Mortimer 3rd Earl March, Earl of Ulster died. He was buried at Wigmore Abbey. [his nephew] Roger Mortimer 4th Earl March 3rd Earl of Ulster succeeded 4th Earl March, 3rd Earl of Ulster, 6th Baron Mortimer of Wigmore.
After 29th January 1386 Thomas Mortimer and Agnes Poynings Baroness Bardolf were married. He the illegitmate son of Roger Mortimer 2nd Earl March.
On 19th December 1387 an army of the Lords Appellant led by the future King Henry IV of England prevented the forces of King Richard II of England commanded by Robert de Vere 1st Duke Ireland from crossing the bridge over the River Thames at Radcot in Oxfordshire. When Thomas of Woodstock 1st Duke of Gloucester arrived with further Lord Appellant's men the King's men were encircled. The King's men attempted to force the crossing of the bridge at which time the only casualties occurred including Thomas Molyneux who was killed by Thomas Mortimer. Around 800 men drowned in the marshes whilst trying to escape. Robert de Vere 1st Duke Ireland narrowly escaped to France.
Walsingham Chronica Majora. 19th December 1387. At that time, there was a certain Thomas Molyneux, who prepared himself for battle, as not all the lords had yet gathered at that place, but only one—Henry, the Earl of Derby, son of the Duke of Lancaster. After fighting for some time, Henry, exhausted and despairing, entered the nearby river. Among the many present, Thomas de Mortimer, a knight, urged him either to come ashore or be pierced with arrows in the river without a doubt. "If I come ashore," said Thomas, "will you spare my life?" "I make no such promise," replied the knight, "but either come ashore or you will soon perish." To this, Thomas responded, "If that is the case, allow me to come ashore and fight you or any one of you, so that I may die as a man." As he began to ascend, the knight grabbed him by the helmet and pulled it off his head. Immediately, drawing a dagger, the knight pierced Thomas' brain, killing him.
Erat ibi tune dictus Thomas Mulinewes, qui se praparavit ad pugnam, quia nondum Domini cuncti convenerant ad illum locum, sed unus tantum, filius Ducis Lancastriæ, Henricus, Comes Derbeyæ; qui, cum aliquandin pugnasset, fessus et desperans flumen, quod prope erat, ingressus est. Inter multos vero, Thomas de Mortuo Mari, miles, hortabatur ut ascenderet, vel sine dubio eum in flumine sagittis perforaret. "Si," inquit Thomas, "ascendam, visne servare vitam meam?" "Non hoc promitto," ait miles, "sed vel ascendas vel occumbes mox." Cui ille,—"Si sic," inquit, "necesse est, sinas ut ascendam et tecum, vel quocunque vestrum, pugnem, ut moriar sicut homo." In ascendendo autem cepit eum miles per cassidem, et de capite suo traxit, et mox, extracto cultello daggardo, ejus cerebrum perforavit.
Westminster Chronicle. Therefore, on the twentieth day of December, the aforesaid duke, making his journey with his Cheshiremen and Welshmen, numbering five thousand, towards Witney, was first met in a broad field by the earl of Arundel with his men. Seeing them, the aforesaid duke encouraged his men to battle, drew them up for the fight in distinct battle-lines, and raised the banners of the king and of Saint George. When the earl of Arundel and the other lords who were then present learned this, they sent to them, saying that they held with the king as his liege men, and that they did not wish to fight against them in any way unless they meant wholly to stand with the traitors of the king and kingdom, who had been lawfully appealed on certain charges of treason. But they answered and said that they had by no means come for the sake of fighting, but that, by the king’s command, for the protection of the person of the duke of Ireland, "know that we have ridden together with him. But we do not wish to give aid to the traitors of the king or kingdom, nor to provide them with help in anything." Therefore they immediately showed signs of peace, lowering their bows and their other arms. The lords then ordered them to return to their homes, and not to proceed any further with the aforesaid duke in any way, if they wished to save their lives. Sir Thomas Mortimer1, however, notwithstanding the negotiation, rushed upon a certain man called Molyneux, the chief counsellor of the aforesaid duke, and immediately killed him.
Then the other lords came to the said place with their companies of armed men, those who had been farther away from that place than the rest, arranging themselves as though they were about to enter into mortal combat. The duke, therefore, astonished at this sight, and perceiving that his men had been defeated, took flight and came to the bridge called Radcot Bridge, which he found broken. Therefore, on horseback, he entered the River Thames, and having swum across the channel, vanished from their sight. In that deep water some of his men were drowned, and very many there, near the river-bed, were also trampled down in the marshes by those pursuing the aforesaid duke. The rest, having lost their arms and their horses, returned sorrowfully to their own homes. All the baggage and equipment of the aforesaid duke was brought to the lords. The duke of Ireland, having thus escaped from the hands of the lords, went to the king in the clothing of a groom or servant. After having such conversation with him as he could, he quickly went to the castle of Queenborough. There, having at once secured a ship, he withdrew to the lands beyond the sea.
Igitur xx die Decembris dux prædictus iter faciens eum suis Cestrensibus et Walensibus numero quinque millia versus Wytteneyam ubi in lato campo primo cum suis comes Arundelliæ occurrebat quos videns dux prædietus animavit suos ad bellum distinetis aciebus ad pugnam erexitque vexilla regis et sancti Georgii. Quod comperiens comes Arundelliæ et cæteri domini qui tunc aderant miserunt ad illos dicentes se tenere cum rege sicuti suos ligios homines, nec velle contra illos ullatenus dimicare nisi voluerint omnino stare cum regis et regni proditoribus qui sunt super certis proditionibus legitime appellati. At illi respondentes dixerunt se nullatenus causa pugnæ venisse sed jussu regis gratia tuitionis personæ ducis Hiberniæ noverint nos seeum pariter cequitasse, proditoribus vero regis seu regni opem impendere nolle nec in aliquc juvamen præstare. Unde protinus ostenderunt signa pacis erectis areubus et eorum cæteris armamentis. Quos tunc jusserunt domini ad eorum larves redire nec cum duce prædicto debere ulterius procedere ullo modo si voluerint eorum vitam salvare. Dominus vero Thomas de Mortuo Mari non obstante tractatu irruit in quendam vocatam Molineres præcipuum consiliarium ducis prædicti et ipsum protinus interfecit.
Tunc vero venerunt ad dictum locum cæteri domini cum eorum cuneis armatorum qui ab eo loco cæteris remotiores fuerunt disponendo se tanquam inirent certamen mortale. Dux itaque ad hujusmodi spectaculum stupefactus perpendensque suos fore devictos fugam arripuit venitque ad pontem vocatum Rodecotebrygg, quem fractum invenit ; igitur eques flumen Thamysiæ intravit transnatatoque alveo ab oculis eorum evanuit. In illo enim gurgite quidam de suis erant submersi et quamplures ibi prope alveum in paludibus ab insequentibus ducem prædictum fuerant etiam conculcati. Cæteris vero armis amissis atque eorum equis dolentes ad propria redierunt. Supellectilia itaque omnia præfati ducis ad dominos sunt adducta. Dux itaque Hibernicus taliter a manibus dominorum evasus in habitu garcionis ad regem accessit, habitoque colloquio tali quali cum eo celeriter adiit castrum de Queneborgh. Ubi confestim navigio perquisito in partes transmarinas secessit.
Note 1. Thomas Mortimer, around 1350-1399, killed Thomas Molyneux, around 13380-1387. Walsingham, St Albans Chronicle: The Chronica Maiora: "At that time, there was a certain Thomas Molyneux, who prepared himself for battle, as not all the lords had yet gathered at that place, but only one, Henry, the Earl of Derby, son of the Duke of Lancaster. After fighting for some time, Henry, exhausted and despairing, entered the nearby river. Among the many present, Thomas de Mortimer, a knight, urged him either to come ashore or be pierced with arrows in the river without a doubt. 'If I come ashore,' said Thomas, 'will you spare my life?' 'I make no such promise,' replied the knight, 'but either come ashore or you will soon perish.' To this, Thomas responded, 'If that is the case, allow me to come ashore and fight you or any one of you, so that I may die as a man.' As he began to ascend, the knight grabbed him by the helmet and pulled it off his head. Immediately, drawing a dagger, the knight pierced Thomas."
In 1397 Thomas Mortimer was charged with treason for having killed Thomas Molyneux at the Battle of Radcot Bridge. Ordered to surrender himself with three months he decided to flee to Scotland.
In 1399 Thomas Mortimer died.