He was born in Exeter of a humble family, the son of Thomas Templer a brazier, and was orphaned young whereupon his elder brother apprenticed him to John Bickley, a carpenter or architect of Exeter. He broke his indenture and set off for India where he made a fortune, either from government building contracts or possibly from dealing in silver bullion, before returning to England aged 23. He settled at Rotherhithe, Kent, where he obtained a government contract to re-build the dockyard with his partners John Line and Thomas Parlby, whose sister Mary Parlby became his wife. In about 1760 he and his partners obtained the contract to rebuild Plymouth docks, for which he used granite from Haytor, and moved to Devon. Templer and Parlby also built the Royal Marine Barracks, Stonehouse, Plymouth between 1779 and 1785. In 1763 he obtained a grant of arms from the College of Arms. He adopted the Latin mottoNihil Sine Labore. In 1765 he purchased the estate of Stover, Teigngrace where he built Stover House, probably to his own design. He also acquired other properties including:
Acton House, Middlesex, near London, which he acquired in 1770 from Capt. Charles Burton and was from then on his business headquarters. It was sold in 1786 by his son and heir to James Stratton, and demolished in 1904.
Demesne lands of Somerhill House, Tonbridge, Kent, of about 1,200 acres, which he acquired from Edward Whatmore of Salisbury, and which descended to his son Rev. John Templer.
Reversion expectant on the death of Lady Elizabeth Archer of one third of the Hale Park estate in Hampshire, comprising lands in Hampshire, Wiltshire and Dorset, purchased from Andrew Archer, 2nd Baron Archer in 1776, before division in total 459 hectares. In 1783, shortly after his death, James Templer's heirs obtained a private Act of Parliament to allow them to break the trust established by his will, in order to sell this reversion and to invest the proceeds in lands more conveniently situated in Devon.
Templer married Mary Parlby, the sister of his business partner Thomas Parlby and daughter of John Parlby of Chatham, Kent. They had seven children:
James Templer, eldest son and heir, who built the Stover Canal in 1792 to transport clay along the Teign Estuary from the Bovey Basin to the port of Teignmouth.
Rev. John Templer, 2nd son, Rector of Teigngrace, who in 1778 married Jane Shubrick, the widow of John Line of Lindridge House, Sheriff of Devon in 1774.
William Templer, 3rd son, died aged 25 at Portsmouth, buried at Teigngrace.
Lt-Col.Henry Line Templer, 10th Lt Dragoons and one of the Prince Regent's household.
Charles Beckford Templer, youngest son, who at the age of 15 drowned in the notorious shipwreck of the Halsewell on the Dorset coast, whilst sailing to Bengal.
He died in 1782 and is commemorated by a mural monument in Teigngrace Church, as is his wife. The church was also rebuilt in 1787 by three of his sons in memory of their parents. Pevsner thought highly of this family stating: "The Templers were people of taste, as is clear from the building and their monuments".
