His parents were strong abolitionists and frequently opened their home to escaped slaves heading north along the Underground Railroad.

[5] In 1878,[2] on the recommendation of Edward S. Morse,[6] he was recruited to help the modernization of Meiji Era Japan as one of the o-yatoi gaikokujin (hired foreigners), serving as visiting professor of physics at Tokyo Imperial University.

From measurements using a Kater's pendulum of the force of gravity at sea level and at the summit of Mount Fuji,[7] Mendenhall deduced a value for the mass of the Earth that agreed closely with estimates that Francis Baily had made in England by another method.

He became professor at the U.S. Signal Corps in 1884, introducing of systematic observations of lightning, and investigating methods for determining ground temperatures.

Resigning in 1886, Mendenhall took up the presidency of the Rose Polytechnic Institute in Terre Haute, Indiana before becoming superintendent of the United States Coast and Geodetic Survey in 1889.

The gravimeters were used at over 340 survey stations across the US and around the world including Germany, the Netherlands, Java, Philippines, Cuba, Haiti, Bahamas, Dominican Republic, Panama, Canada, and Mexico.

His portrait is currently part of the Smithsonian Institution National Portrait Gallery in Washington, D.C.[11] It was painted by his former pupil Annie Ware Sabine Siebert, who was the first recipient of a Master of Arts degree from The Ohio State University in 1886, and one of the first women to earn an architecture degree from the Massachusetts Institute of Technology (MIT) in 1888.

[6] In 1887 Mendenhall published one of the earliest attempts at stylometry also known as author profiling, the quantitative analysis of writing style.

[13] Prompted by a suggestion made by the English mathematician Augustus De Morgan in 1851, Mendenhall attempted to characterize the style of different authors through the frequency distribution of words of various lengths.