He entered the Order of Benedictines and by 1238 was dean of the abbey of Saint-André de Villeneuve at Avignon.
On 13 July 1257, he was present at Brignoles at a ceremony of infeudation, between Charles, Count of Anjou, and Gilbert de Baux.
[9] He pronounced the decision in an arbitration, along with Cardinal Vicedomino de Vicedominis, at Lyon on 25 April 1275.
[10] On 7 June 1275, at Bellicadri, he was assigned the Roman titulus of S. Marcello in commendam[11] He apparently did not accompany Pope Gregory X in the return trip from Lyon to Rome.
His name is not mentioned among the cardinals at Lausanne, who witnessed the oath of fealty of King Rudolf I.
The first conclave began in the Episcopal Palace in Arezzo on 21 January, in accordance with the Constitution "Ubi Periculum" of Gregory X.
[19] The third Conclave of 1276, should have begun in Viterbo ten days after the death of Pope Adrian V, according to the Constitution of Gregory X, "Ubi Periculum".
The meeting discussed the problems that had been encountered in the two conclaves that year, and it was agreed that adjustments and additions were needed.
He believed that scriptores and procurators in the Curia were the ringleaders, and if their confessions were not forthcoming within a week, Cardinal Bertrand was to proceed to inquisition.
[22] Pope John XXI was killed suddenly, when the roof of a room in the Episcopal Palace in Viterbo, which had recently been constructed, happened to fall on him.
There were only seven cardinals (Simon de Brion was still Legate in France), and they were bitterly divided, three in the Angevin party, and three in the Imperial.
For a long time it was thought that Cardinal Bertrand de Saint-Martin died during the Second Council of Lyon in 1274 or in 1275, and shortly thereafter was succeeded in the see of Sabina by Giovanni Visconti, nephew of Gregory X.
However, modern research has established that "cardinal Giovanni Visconti" never existed, while Bertrand is attested in the papal documents until the Sede Vacante following the pontificate of John XXI (died in Viterbo on 16 May 1277).
[25] The most probable year of his death seems to be 1278, because contemporary sources mention him as participant in the papal election, 1277, which took place between May and November,[26] and (by inference) in the first consistory of Pope Nicholas III on 12 March 1278.