[5] His ancestor, Barthélémy de Jura, Bishop of Laon, attended the Council of Troyes (1129) which wrote the rule for the Knights Templar.

In return for likely service for Prince Edward at the battles of Lewes and Evesham he was rewarded with property at Queenhithe in London.

According to Jean d’Ypres, it was Otto, not Eleanor of Castile, who sucked the poison from the wounded Edward after an attempted assassination.

During the Welsh Wars of King Edward I Otto was very active diplomatically and militarily, beginning with the siege of Dolforwyn Castle in April 1277.

During the second invasion of Wales in 1282–83 he narrowly escaped death at the battle of Moel-y-don[24] before in April 1283 taking the town of Harlech at the head of 560 infantry.

[25] As a commander of the royal army that had begun the campaign from Anglesey he was amongst the first of Edward’s retinue to see the future castle sites at Caernarfon and Harlech.

At Acre he saved the life of fellow Savoyard Jean I de Grailly, with whom he had served Edward in Gascony earlier.

As the city fell to the Muslims he commandeered Venetian ships filling them with fleeing troops and the wounded Jean I de Grailly, Otto was the last to join them on board.

He commandeered as many Venetian ships as he could find and placed Jean de Grailly and all soldiers he could rescue on board, and himself was the last to join them.”[29] After the fall of the city he fled to Cyprus a poor man, but went on a subsequent pilgrimage to Jerusalem.

[30][31] In his La flor des estoires d'Orient, the Armenian monk Hayton of Corycus mentions his activity on the mainland in Cilicia in 1298–1299: "Otto de Grandison and the Masters of the Temple and of the Hospitallers as well as their convents, who were at that time [1298 or 1299] in these regions [Cilician Armenia] .

[32] Otto has been hypothesised as the author of the Via ad Terram Sanctam, an Old French treatise on the recovery of the Holy Land.

The chronicler of Vale Royal described Grandson in these terms: “Now there was at that time with the King a good and holy man, and a most strenuous knight in arms, named Otto de Grandison, whose memory be blessed for ever.”[41] He founded a Franciscan friary in 1289 and a Carthusian monastery at La Lance in 1317.

I give and bequeath to the church of Lausanne all my ornaments, clothing and silverware which are now deposited there, with the exception of a small gold cross and a statue of the B[lessed].

The payments are thought to relate to the Fall of Acre in 1291 and the subsequent election of Jacques de Molay as Grand Master of the Knights Templar on Cyprus in 1292.