More may be added to the earlier biography.
Trethake does not appear to have become involved in the legal wranglings which followed his father’s death, instead leaving his elder brother John to defend the family property.
Trethake built up a close relationship with the wealthy Sir Otto Trevarthian, whom he served as under sheriff in 1416-17. Trevarthian, however, never repaid Trethake for his services. At the time of his death, Sir Otto not only owed the lawyer his salary of £6 13s. 4d. for his under shrievalty, but also a substantial separate debt of £20. Perhaps through the link with Trevarthian, Trethake later also became connected with the knight’s cousin, the powerful Sir William Bodrugan*, whom he also served as under sheriff in 1427-8 and for whom he attested deeds in 1434.
In February 1427 Trethake joined Robert Treage* as arbiter in a dispute between John Tretherf* and Richard Penpons*. He was later present at the Cornish shire elections in 1436 when both men were elected knights of the shire.
Although there is no definite evidence to suggest that Trethake himself had interests in the tin industry, he nevertheless maintained close contacts among those who did throughout his career. Among his clients in the autumn of 1419 was Richard Hervy* of Lostwithiel, at one time sub bailiff (or ‘tynbaylyf’) of Blackmore stannary, and the tin trade may also have played a part in his disagreement in about 1433 with the Lostwithiel merchant Roger Wolley.
Trethake was certainly dead by the end of 1442, when John Trethake, either his brother or another kinsman of the same name, was engaged in the execution of his will.