Robert C. Harder was born on 4 June 1929 at Horton, Kansas to the Reverend and Mrs. Clarence Harder. After graduating from Troy High School in 1947, he attended Baker University (Kansas), receiving his A.B. in 1951; he then went on to earn a Master of Theology at Southern Methodist University in 1954 and a Doctor of Theology at Boston University in 1958. After graduating, Harder returned to Kansas, serving as pastor of the East Topeka Methodist Church from 1958-1964. During his time as a pastor, Harder was active in various community groups, such as the Topeka Day Care Association and the East Topeka Civic Association, with which he continued to work even after leaving the pulpit.

Harder soon became involved in Kansas state politics. From 1961-1967, he served as a State Representative, a position that led to other government positions. Those positions included: Director of the Topeka Office of Economic Opportunity; the Technical Assistance Coordinator for Governor Robert Docking; Projects Administrator of Topeka State Hospital; Secretary of the Department of Health and Environment; and Director of the State Department of Social Welfare, which was later reorganized into the State Department of Social and Rehabilitation Services where Harder was appointed as the new department's first Secretary. His consumer advocacy regarding Medicaid, welfare, social services, and state health programs continued beyond his retirement, as a volunteer lobbyist for the Kansas United Methodist Church and as an advocate for children, families, and the poor.

At various times throughout his career, Harder also worked as a research assistant and, later, as a consultant for the Menninger Foundation; as an instructor at Washburn University; and as an Adjunct Professor at the University of Kansas. Harder's numerous service organizations have included the Topeka Association for Retarded Citizens and the Shawnee County Association for Mental Health. His leadership in various organizations included membership on the Board of Trustees of Baker University and on the Board of Directors of the Kansas Committee for the Prevention of Child Abuse and the Kansas Statewide Independent Living Council. Harder's many awards for service include the Martin Luther King, Jr. Living the Dream Humanitarian Award (1997) and the Kansas Friends of Education Community Leader Award (2004).

Harder married Dorothy Lou Welty in 1953. Their children are Anne and James David.