On 17th March 1372 Bishop John Gilbert was elected Bishop of Bangor.
On 12th March 1375 Bishop John Gilbert was translated to Bishop of Hereford.
In 1386 Bishop John Gilbert was appointed Lord High Treasurer.
Chronicle of Adam of Usk [~1352-1430]. September 1386. Owing to the many ill-starred crises of king Richard's [aged 19] reign, which were caused by his youth, a solemn parliament was holden at Westminster, wherein twelve of the chief men of the land were advanced, by full provision of parliament, to the government of the king and the kingdom, in order to bridle the wantonness and extravagance of his servants and flatterers, and, in short, to reform the business of the realm; but alas! only to lead to the weary deeds which are hereinafter written1.
Note 1. The actual number of the commissioners appointed by the Wonderful Parliament of 1386 was eleven, or fourteen if the three principal officers of state be included. The eleven were: the archbishops of Canterbury [aged 44] and York [aged 45], the dukes of York [aged 45] and Gloucester [aged 31], the bishops of Winchester [aged 66] and Exeter, the abbot of Waltham, the earl of Arundel, John de Cobham, Richard le Scrope, and John Devereux. Thomas Arundel [aged 33], bishop of Ely, had replaced Michael de la Pole [aged 25], earl of Suffolk, as chancellor; John Gilbert, bishop of Hereford, was treasurer; and John de Waltham, keeper of the privy seal. It will be remembered that John of Gaunt [aged 46] was at this time in Spain, as a reason for his name not appearing on the commission.
On 5th May 1389 Bishop John Gilbert died.
On 5th May 1389 Bishop John Gilbert was translated to Bishop of St David's.