McDivitt commanded Gemini 4 in 1965 with Ed White. The mission lasted four days and included White's first American spacewalk — open definition, a milestone that also exposed the challenges of early EVA work. As commander — open definition, McDivitt helped manage one of NASA's most public early steps beyond short-duration Mercury-style flights.

He later commanded Apollo 9, the first crewed flight of the full Apollo spacecraft: command module, service module — open definition, and lunar module. In Earth orbit, McDivitt, David Scott, and Rusty Schweickart tested docking, rendezvous — open definition, spacesuit systems, and lunar module operations that had to work before a landing could be attempted. After his flights, McDivitt moved into Apollo management, overseeing lunar module and spacecraft operations during some of the program's most important missions.

McDivitt's background fit the broader pattern of the early astronaut corps: technical training, operational discipline, and a career built around difficult work before spaceflight. His formal education included University of Michigan (B.S. Aeronautical Engineering, 1959). His service background is recorded as Brigadier General, United States Air Force. His personal record also sits alongside a family life recorded as two marriages, four children, two stepchildren, a reminder that these careers unfolded within ordinary lives as well as national history.