Born in Brasher Falls, New York, Sanborn moved with his parents to Wisconsin in 1857, settling in Lake Geneva.

He was self-educated, and, when the family moved to Elkhorn, the county seat, in 1869, he was able to obtain employment as a clerk in the office of the Register of Deeds.

[1] During this period, Sanborn was also employed as a professor of law on the faculty of the University of Wisconsin, and served on the state board of bar examiners.

[2][3][4] Sanborn was the Republican candidate for mayor of Madison in 1890, but was defeated by city attorney Robert McKee Bashford.

Sanborn was confirmed by the United States Senate on January 9, 1905, and received his commission the same day.