Born in Worcester, Washington County, Vermont, Templeton was of English descent, his ancestors being among the early colonists of New England.

He then entered Dartmouth College, where he "was quite prominent in athletics, taking numerous prizes", graduating on June 27, 1878, and thereafter reading law in the office of S. C. Shurtleff to gain admission to the bar in Montpelier, Vermont, on December 6, 1880.

[2] On March 12, 1887, he was appointed Attorney-General of Dakota by Territorial Governor Louis K. Church.

He resigned on November 10, 1888, to accept an appointment from President Grover Cleveland as an Associate Justice of the Dakota Territorial Supreme Court.

[3] He resumed the practice of law in Grand Forks until 1907, when Governor John Burke appointed Templeton to again serve as Judge of the First Judicial District of North Dakota.