The following information taken from Medieval English Genealogy website at:
http://www.medievalgenealogy.org.uk/families/arg/argoutl1.shtml
According to his father's Inquisition Post Mortem, John de Argentein was aged 30 when he succeeded his father in 1308 (Calendar of Inquisitions Post Mortem). Presumably this is a round figure, so that John would have been born in the late 1260s or in the 1270s - probably after his father's release from captivity after the Battle of Evesham, at any rate.
We first hear of John when, at his marriage to Joan, the daughter of Roger Brian in 1302, settlements were made by their parents. Reginald settled the manor of Fordham (in Essex) on the couple, and Roger settled his manors of Hatley (in Bedfordshire) and Throcking (in Hertfordshire) after his death. (Roger seems to have died by 1307, when John had a grant of free warren in Hatley and Throcking (Charter Roll)). By his first wife, John had three daughters:
Joan, born c.1310
Elizabeth, born c.1312
Denise, born c.1315
(Calendar of Inquisitions Post Mortem). We know that Joan must have died soon after the birth of Denise, leaving her daughters to inherit the Brian estates.
Four Argentein gravestones, apparently in Baldock church, are recorded in Sloane MS 1301 (fo.146b). In addition to those of Reginald and Lora are two more, bearing the names 'Iohn de Argentine' and 'Iohan de Argentine'. It seems likely that these are the gravestones of Reginald's son John and his first wife, Joan. If so, the arms illustrated ('Gules a saltire [?]or, a chief ermine') must be those of the Brian family, although I have not seen them recorded elsewhere under this name.
Some interesting light is shed on the family's domestic arrangements by a surviving set of accounts for 1317-8 from the manor of Melbourn (Palmer), where they seem to have been living at the time. We know from later evidence that Joan's elder daughters, Joan and Elizabeth were married to two brothers, John and William, the sons of Ralph Boteler (or Butler). (The younger daughter, Denise, died without issue.) Evidently they were married extremely young. In fact, the marriages must have been arranged immediately after their status as heiresses was apparent, because in the Melbourn accounts occurs an 'Aid for marrying the lord's eldest daughter'. The young bridegrooms also seem to have been living at Melbourn: the accounts also contain expenses for 'little socks', 'shoes' and 'slippers' for John Boteller, and 'linen cloth for the use of John Boteller and his brother'.
By April 1317, John had remarried, to Agnes, the daughter of William de Bereford (Hertfordshire Record Office, no 59315). The following Spring, Agnes gave birth to a son, John, who was to succeed his father at the age of 6 months. The Melbourn accounts include an entry 'for four score and four geese and goslings (hocorys) bought for the churching feast of the Lady Agnes' after John's birth (Palmer).
In contrast to his 13th-century ancestors, John de Argentein's official roles were purely local (although he might perhaps have achieved greater prominence if he had lived longer). He had a commission of oyer and terminer in 1312, after a band of robbers had assaulted and robbed a representative of the king at Baldock (Patent Roll), and others in 1316 and March 1318 concerning disturbances in Cambridgeshire (Patent Roll). In 1314 he had been appointed one of the conservators of the peace for Hertfordshire (Patent Roll), and in November 1317 he was appointed to a commission in Hertfordshire to enquire into those raising bodies of men-at-arms (Patent Roll).
In the military sphere, John's arms ('de goules a iii.coupes de argent') appear in the roll prepared for the first Dunstable tournament in 1308 (Parliamentary Writs). The Melbourn accounts of 1317-8 also show him undertaking a journey to the north ('a horse bought for Jackbet when he went north with my lord' (p.44); 'for saddle gerthys for the lord when he went north' (p.54)), which Palmer suggests would have been for military service against the Scots. It is not clear whether he ever returned from this journey.
John died, apparently only in his 40s, shortly before 20 October 1318 (Calendar of Inquisitions Post Mortem), leaving his second wife Agnes and her baby son. As mentioned above, he was possibly buried in Baldock church, although another account says that his gravestone was formerly in Little Wymondley church, having possibly been removed there from Wymondley Priory (Wright, p.143). (Some support is lent to this by the provision in his widow Agnes's will to be buried in the Priory if she dies in Hertfordshire or Cambridgeshire, though nothing is said about John Argentein's place of burial.)