Richard was a scion of a lesser Cornish gentry family closely connected with the powerful Arundells of Lanherne.
Tresithney is not known to have distinguished himself in the Commons and never held office under the Crown or in the service of the duchy of Cornwall, although he did on occasion serve on local juries.
Perhaps through his putative father, by the mid 1430s Tresithney had been drawn into the lengthy and violent dispute between Robert Borlase and the brutal Richard Tregoose*. In early 1444 Tregoose claimed before the justices of common pleas that in September 1433 Tresithney had conspired with Borlase, Sir John Arundell II*, John Tresithney and others to have him indicted of cattle theft before the justices of oyer and terminer, and had succeeded in having him arrested and placed in the marshalsea of the King’s bench. In parallel, so Tregoose alleged, the two Tresithneys had fabricated additional charges against him, accusing him of the rape and abduction of the young daughter of one of the earl of Warwick’s villeins. At the Launceston assizes in August 1445 a jury found in favour of Tregoose, and awarded the vast sum of £1,000 in damages against Tresithney and his associates.
It is not known whether Tresithney was ever forced to pay a share of these damages, and he may have died not long after. The date of his death is not recorded, but he seems to have predeceased his wife, Joan, who was also dead by October 1446, when her heir was fined for failing to pay suit to the manor court of Trenant.
