A native of the parish of Sithney, Treloar was born on 26 December 1814 to Thomas Treloar and Jenifer Martin. Following his marriage to Allarina Symons of Helston in February 1834, the newly weds sailed from Falmouth aboard the Alexander Penny for Rio de Janeiro and the gold mines of the Coaces Mining Company. He remained there for several years until returning to Cornwall to be hired as Mine Captain in 1843 by the Imperial Brazilian Mining Company for their Gongo Soco mine. In 1845 he accepted the position of head mining captain at the Morro Velho mine of the St John del Rey Mining Company which saw a period of remarkable prosperity under his captaincy.
He resigned his position with the company in 1862 after a bitter row with the superintendent, James Newell Gordon, over the method of working the mine, part of which collapsed in 1867 seemingly confirming his concerns. He visited England briefly before returning to Brazil where he became chief engineer to the Don Pedro North del Rey Gold Mining Company by 1864, returning to Cornwall to hand pick miners for this enterprise in 1868. His wife, by whom he had 12 children, died in 1867. Most of their daughters were sent back to Cornwall between 1851 and 1861 to be educated, residing at Helston first with their aunt Susan Symons, then their grandmother Jenifer Treloar.
Credited with the discovery of rich deposits of gold in the Jacotinga Maquine Mine he received a gift of £1,000 in 1869 as a token of appreciation for his services to the company. Treloar became involved in a number of mining operations with his sons-in-laws Francis Stanfield Symons and Thomas Tregellas. So successful were they that they roused the envy and animosity of many who resented their good fortune: 'they are looked upon as little better than thieves. Buying properties at three times their value for companies and pocketing the difference. All the mines which have come to grief have been under their hands, or sons in law of the old Treloars' noted Stonehewer Edward Illingworth in his journal of the early 1870s.
In the late 1860s Treloar successfully obtained the workings of the Itabira mining sett for the General Brazilian Mining Company. The Anglo Brazilian Times in 1871 reported on a splendid ball thrown in honour of 'the Brazilian Gold King', by the leading citizens of Itabira upon his impending departure for England. In spite of unfavourable comments such as the above, a transparency was placed over his chair at this event declaring 'the right man in the right place'. When he left for England all the gentry in the city and suburbs accompanied him on part of the journey. He died at Clapham Common London in 1880 after a long and painful illness.