Franklin Ramón Chang Díaz was born in San José, Costa Rica on April 5, 1950 to a Costa Rican father of Chinese descent, Ramón Ángel Chang Morales, an oil worker whose own father fled China during the Boxer Rebellion. His mother is also Costa Rican, María Eugenia Díaz Romero. One of six children, he has a younger sister, Sonia Rosa (born December 1952) and his mother, brothers and sisters live in Portland. His elder daughters are Jean Elizabeth (born December 1973) and Sonia Rosa (born March 1978) who is a member of the Massachusetts Senate. He married in the United States, on 17 December 1984, interior designer Dr. Peggy Marguerite Doncaster (née Stafford, of Alexandria, Louisiana), the founder of Stafford Tile and Stone, and his younger daughters are Lidia Aurora (born March 1988) and Miranda Karina (July 1995), both born in Houston, Texas.

He graduated from Colegio de La Salle in San Jose with an “A” in November 1967, then moved to the United States to finish his high school education at Hartford Public High School in Connecticut, in 1969. He went on to attend the University of Connecticut, where he earned a B.S. degree in mechanical engineering and joined the federal TRIO Student Support Services program in 1973. He then attended the Massachusetts Institute of Technology (MIT), where he earned a Ph.D. degree in applied plasma physics in 1977. For his graduate research at MIT, Chang Díaz worked in the field of fusion technology and plasma-based rocket propulsion.

Chang Díaz was selected as an astronaut candidate by NASA in 1980 and first flew aboard Space Shuttle mission STS-61-C in 1986. Subsequent missions included STS-34 (1989), STS-46 (1992), STS-60 (1994), STS-75 (1996), STS-91 (1998), and STS-111 (2002). During STS-111, he performed three extra-vehicular activities (EVAs) with Philippe Perrin as part of the construction of the International Space Station. He was also director of the Advanced Space Propulsion Laboratory at the Johnson Space Center from 1993 to 2005. Chang Díaz retired from NASA in 2005.

In 1986, Franklin Chang Díaz was one of twelve recipients of the Medal of Liberty. He was inducted into the NASA Astronaut Hall of Fame on May 5, 2012 in a ceremony that took place in the Kennedy Space Center Visitor Complex. Also, due to his career and scientific success, he has been decorated multiple times in Costa Rica and named Honor Citizen by the national legislature. The Costa Rican National High Technology Center (CeNAT), among other institutions, is named after him. In 2014, Chang Díaz was awarded the “Buzz Aldrin Quadrennial Space Award” by The Explorers Club. Buzz Aldrin, whom Chang Díaz called a childhood hero, presented the award.