After attending the common schools, Valentine began his business career in 1854 working for Younglove Brothers, druggists and agents for Carter, Thomas & Company's express line in Bowling Green.

Soon after, he was transferred to Virginia City, Nevada, as agent for Wells Fargo, the Pioneer Stage Line and John Butterfield's Overland Mail Company.

In 1888, as general superintendent he successfully linked up a through express line from the Atlantic Ocean in New York City to the Pacific at San Francisco.

[2]: 255 [4] His annually published summary of the American production of gold and silver was comprehensive in its research and recognized as authoritative on the subject.

Opposed to the free coinage of silver as likely to cause a glut in the domestic market and depreciate its value, in 1891 Valentine's contributions to the press on the subject were notable for close reasoning, careful research, and a formidable array of statistics in support of his conclusions.

[2]: 339  Valentine wrote a number of pamphlets on financial subjects, notably, one titled Money that advocated a parity of value to be maintained between gold and silver.

California Bishop Nichols spoke of Valentine as the 'honored and honest head' of a large corporation who was 'Christian in conviction, in conduct' and who had a 'warm heart for his fellow man.'

The church contains a phenomenal glass window commemorating his wife Mary F. Valentine and two of their children who died at 2+1⁄2 years old and 10 months old.