Mendenhall was born in Hanoverton, Ohio, to Stephen Mendenhall, a farmer and carriage-maker, and Mary Thomas.
In 1852 the family moved to Marlboro, a Quaker community outside of Akron, Ohio.
His parents were strong abolitionists and frequently opened their home to escaped slaves heading north along the Underground Railroad.
Mendenhall became principal of the local primary school in 1858.
He formalized his teaching qualifications at National Normal University in 1861 with an Instructor Normalis degree.

While living in Columbus, Ohio, he married Susan Allan Marple in 1870.
The couple had one child, Charles Elwood Mendenhall (1872–1935), teacher and chairman of the Physics Department at University of Wisconsin–Madison for 34 years.

He taught at a number of schools in Ohio including Central High School in Columbus, gaining an impressive reputation as a teacher and educator.
In 1873, although he lacked conventional academic credentials, he was appointed professor of physics and mechanics at the Ohio Agricultural and Mechanical College.
The college ultimately became The Ohio State University, Mendenhall being the first member of the original faculty.
He was later awarded the first ever honorary Ph.D. from The Ohio State University in 1878.

In 1878, on the recommendation of Edward S. Morse, 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.
In connection with this appointment, he founded a meteorological observatory to make systematic observations during his residence in Japan.
From measurements using a Kater's pendulum of the force of gravity at sea level and at the summit of Mount Fuji, 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 also made a series of elaborate measurements of the wavelengths of the solar spectrum by means of a large spectrometer.
He also became interested in earthquakes while in Japan, and was one of the founders of the Seismological Society of Japan (SSJ).
During his time in Japan, he also gave public lectures on various scientific topics to general audiences in temples and in theaters.

Returning to Ohio in 1881, Mendenhall was instrumental in developing the Ohio State Meteorological Service.
He devised a system of weather signals for display on railroad trains.
This method became general throughout the United States and Canada.

He became professor at the U.S. Signal Corps in 1884, introducing of systematic observations of lightning, and investigating methods for determining ground temperatures.
He was the first to establish stations in the United States for the systematic observation of earthquake phenomena.
Resigning in 1886, Mendenhall took up the presidency of the Rose Polytechnic Institute in Terre Haute, Indiana before becoming superintendent of the U.S. Coast and Geodetic Survey in 1889.
During his time as superintendent, he issued the Mendenhall Order and oversaw the consequent transition of the United States's weights and measures from the customary system, based on that of England, to the metric system.
Mendenhall remained a strong proponent for the official adoption of the metric system all his life.
Also, as superintendent of the U.S. Coast and Geodetic Survey, he was also responsible for defining the exact national boundary between Alaska and Canada.
The Mendenhall Valley and Glacier in Juneau, Alaska was named for him in 1892.

Mendenhall invented the portable Mendenhall Gravimeter in 1890 while he was superintendent of the U.S. Coast and Geodetic Survey, and at that time it provided the most accurate relative measurements of the local gravitational field of the Earth.
The gravimeters were used at over 340 survey stations across the US and around the world including Germany, Holland, Java, Philippines, Cuba, Haiti, Bahamas, Dominican Republic, Panama, Canada, and Mexico.
The swing of the pendulum was more regular than the most accurate clocks of the era, and
Mendenhall was born in Hanoverton, Ohio, to Stephen Mendenhall, a farmer and carriage-maker, and Mary Thomas. In 1852 the family moved to Marlboro, a Quaker community outside of Akron, Ohio. His parents were strong abolitionists and frequently opened their home to escaped slaves heading north along the Underground Railroad. Mendenhall became principal of the local primary school in 1858. He formalized his teaching qualifications at National Normal University in 1861 with an Instructor Normalis degree.
While living in Columbus, Ohio, he married Susan Allan Marple in 1870. The couple had one child, Charles Elwood Mendenhall (1872–1935), teacher and chairman of the Physics Department at University of Wisconsin–Madison for 34 years.
He taught at a number of schools in Ohio including Central High School in Columbus, gaining an impressive reputation as a teacher and educator. In 1873, although he lacked conventional academic credentials, he was appointed professor of physics and mechanics at the Ohio Agricultural and Mechanical College. The college ultimately became The Ohio State University, Mendenhall being the first member of the original faculty. He was later awarded the first ever honorary Ph.D. from The Ohio State University in 1878.
In 1878, on the recommendation of Edward S. Morse, 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. In connection with this appointment, he founded a meteorological observatory to make systematic observations during his residence in Japan. From measurements using a Kater's pendulum of the force of gravity at sea level and at the summit of Mount Fuji, 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 also made a series of elaborate measurements of the wavelengths of the solar spectrum by means of a large spectrometer. He also became interested in earthquakes while in Japan, and was one of the founders of the Seismological Society of Japan (SSJ). During his time in Japan, he also gave public lectures on various scientific topics to general audiences in temples and in theaters.
Returning to Ohio in 1881, Mendenhall was instrumental in developing the Ohio State Meteorological Service. He devised a system of weather signals for display on railroad trains. This method became general throughout the United States and Canada.
He became professor at the U.S. Signal Corps in 1884, introducing of systematic observations of lightning, and investigating methods for determining ground temperatures. He was the first to establish stations in the United States for the systematic observation of earthquake phenomena. Resigning in 1886, Mendenhall took up the presidency of the Rose Polytechnic Institute in Terre Haute, Indiana before becoming superintendent of the U.S. Coast and Geodetic Survey in 1889. During his time as superintendent, he issued the Mendenhall Order and oversaw the consequent transition of the United States's weights and measures from the customary system, based on that of England, to the metric system. Mendenhall remained a strong proponent for the official adoption of the metric system all his life. Also, as superintendent of the U.S. Coast and Geodetic Survey, he was also responsible for defining the exact national boundary between Alaska and Canada. The Mendenhall Valley and Glacier in Juneau, Alaska was named for him in 1892.
Mendenhall invented the portable Mendenhall Gravimeter in 1890 while he was superintendent of the U.S. Coast and Geodetic Survey, and at that time it provided the most accurate relative measurements of the local gravitational field of the Earth. The gravimeters were used at over 340 survey stations across the US and around the world including Germany, Holland, Java, Philippines, Cuba, Haiti, Bahamas, Dominican Republic, Panama, Canada, and Mexico. The swing of the pendulum was more regular than the most accurate clocks of the era, and 
Thomas Corwin Mendenhall