Hadley was born in 1936 and grew up near Thomasville at Pebble Hill, a former cotton plantation in Thomas County, Georgia. At the time of Hadley's birth, Pebble Hill was mainly used for hunting. He was the tenth of 15 children, and is the grandson of a slave who worked at Pebble Hill.
After graduating from high school, he joined the United States Air Force, where he worked with supplies and logistics. He has been married for more than sixty years and has three children. His tenure included postings in Europe, the Middle East and Vietnam. After 28 years he retired with the rank of chief master sergeant. The family moved back to Thomasville and Hadley started working for the United States Postal Service, until his retirement in 1997.
Hadley is a Prince Hall Freemason. In 2018, Thomas University awarded him an honorary bachelor's degree in business administration, in recognition of his work in the Air Force and the community.
Hadley began collecting newspaper clippings on the assassination of Martin Luther King Jr. in 1968, and in the late 1970s he helped his son with a schoolproject about black history. This grew his interest in black history, and he was later invited to participate in Black History Month events in Thomasville. He started collecting memorabilia, which in time became the collection of his museum.
Hadley founded the museum in 1995; in 2006 it opened at its current location, a former school in Thomasville. The museum has received grants to "provide educational programming for school students in the Thomas County and Thomasville City School systems", and in 2019 it started an education pilot program in cooperation with Thomas County Middle School. As of 2019, the museum has more than 4,000 items.
The museum has had more than 18,000 visitors since 2006, and reported nearly 4,000 visitors in 2018. In 2017, Hadley, his family and the museum were honored in a resolution from the Georgia House of Representatives. Wayne Clough, former Secretary of the Smithsonian, praised the museum after visiting.
Hadley also created the "Thomasville Black Heritage Trail Tour", a "step-on, step-off" tour which focuses on Henry Ossian Flipper (1856–1940), an American soldier and former slave. The museum successfully advocated the creation of a commemorative postage stamp for Flipper, as well as naming a Thomasville post office after him.
Following the attention garnered by the 2018 film Green Book, Hadley involved himself in an attempt to restore the Imperial Hotel, a Thomasville building included in The Negro Travelers' Green Book, a travel guide for African-Americans listing places that would not refuse them service. Hadley commented that had he known about the book in the 1960s, it would have been helpful to him, since he often had to drive long distances and at times was turned away because he was black.
There are plans to make part of the Imperial Hotel a "satellite site" of the Jack Hadley Black History Museum, and as of October 2019, over $190,000 had been raised for the restoration. A group of historians led by Hadley has purchased the building, the city's only black-owned hotel. In October 2019, the efforts received recognition from Thomasville Landmarks, a local historical society.
Total Visitors to the Museum 2018 3,769