The Monk of St.-Denys asserts that Knolles shared in the Flemish expedition of Henry Despenser [q. v.], bishop of Norwich, in 1383, and represents him as playing the part at Bergues which Froissart more correctly ascribes to Sir Hugh de Calveley (Chron. Rel. de St.-Denys, i. 258, 270, 272, Documents Inédits, &c.; Froissart, viii. 442–4, ed. Buchon). Probably the remainder of his long life was spent in quiet retirement either in London or at his manorhouse at Sculthorpe, Norfolk. In 1384 there was a serious riot in London under one John Comerton; by Knolles's advice one of the ringleaders was beheaded, and the movement subsided. On 18 Aug. 1389 Knolles had license to go to Rome on a matter of conscience (Fœdera, iii. pt. iv. p. 46). The ‘regal wealth’ (Walsingham, i. 286) which he had amassed in the wars enabled him to acquire large estates, chiefly in Norfolk, but also in Wiltshire, Kent, and London (Cal. Inq. p. m. ii. 305; Hasted, Hist. of Kent, ii. 674; Rot. Parl. iii. 258 b). He frequently assisted Richard II by loans on the security of jewels and plate (Blomefield, vi. 176). His munificence was notable. In 1380 he joined with Sir John Hawkwood and Calveley in the foundation of an English hospital at Rome (Harl. MS. 2111, f. 100 b). In 1388, together with John de Cobham, he rebuilt and endowed the bridge and chantry at Rochester; the bridge was destroyed in 1856 (Eulog. Hist. iii. 367; Rot. Parl. iii. 289 b; Hasted, Hist. of Kent, ii. 17–18). In London he was a liberal benefactor to the house of the Carmelites at Whitefriars, and in Norfolk he rebuilt the churches of Sculthorpe and Harpley; but his chief foundation was a college and hospital for a master, six priests, and thirteen poor men and women, at Pontefract, which was known as ‘Knolles' Almeshouse.’ The college was endowed with 180l. a year, from land chiefly in London and Norfolk; it was dissolved at the Reformation, but the almshouse, revived in 1563, still exists (Blomefield, vi. 21, 276; Cal. Rot. Pat. pp. 211, 220; Rot. Parl. v. 135, 306; Leland, Itinerary, i. 43; Dugdale, Monasticon, vi. 713–14).
Knolles died at Sculthorpe 15 Aug. 1407, and was buried at Whitefriars, London (Weever, Funerall Monuments, p. 436; Coll. Top. et Gen. viii. 321). His two wills in French and Latin, and dated 21 Oct. 1399 and 20 May 1404 respectively, are now extant at Lambeth. No mention is made of any children (Herald and Genealogist, viii. 289). As a soldier he must be placed among the most eminent of his age; Froissart speaks of him as ‘the most able and skilful man of arms in all the companies,’ and says that he was chosen for the command in 1370 on account of his great skill and knowledge in handling and governing an army (iv. 186, vii. 223). His partial ill-success on that occasion was due to prejudices which he could scarcely have controlled, and he seems to have possessed some of the qualities of a true general as distinguished from a merely skilful soldier. In his own time and country he was scarcely less renowned than Hawkwood, whom he might have rivalled permanently but for his loyalty to his sovereign and his native land—a characteristic specially mentioned by Froissart (vii. 139). To Cuvélier he is ‘Robert Canole qui moult greva Françoiz tous les jours de sa vie’ … ‘qui ne prise Françoiz deux deniers seulement’ (i. 101, ii. 163). The Chandos herald calls him ‘a man of few words’ (ed. Coxe, l. 2725).
Knolles was married to his wife Constantia before 1360 (Fœdera, iii. 480). Leland says that she was a native of Pontefract and ‘a woman of mene birth and sometime of a dissolute lyvyng before marriage’ (Itinerary, i. 43). But her arms, ‘argent a fess dancette between three pards' faces sable,’ are those of the Yorkshire family of Beverley, to which she perhaps belonged (Coll. Top. et Gen. viii. 321). Dying a few days after her husband, she was buried by his side. Sir Robert left no legitimate male heirs, and it is very doubtful whether he was even, as some have supposed, the father of Emme or Margaret Knolles who married John Babington of Aldrington, Devon (Herald and Genealogist, v. 296; Blomefield, vi. 175). Sir Robert's name most usually appears in contemporary English writers as Knolles, but Knollis, Knowles, and Knollys also occur. French writers usually call him Canolles or Canole. The common statement that he was a knight of the Garter is not substantiated (Anstis, Register of the Order of the Garter, ii. 30–2).