Carol Ann O'Neale of Alexandria, Virginia, was born on June 14, 1947, to parents William Leroy O’Neale and Ada Esther Vandenberg. Attending Mount Vernon High School and later graduating from Fort Hunt High School in 1965, O'Neale participated in many extracurriculars, including art club, French club, class council, and majorettes. In 1970, she obtained a bachelor's degree from the College of Architecture at Virginia Tech. Shortly after graduation, on September 3, 1970, O'Neale married fellow Virginia Tech School of Architecture graduate Kenneth S. Culnan, and changed her name to Carol O'Neale Culnan.

In the early 1970s the couple moved into a row house on Swann Street NW near Dupont Circle in Washington, D.C., and performed a gut rehabilitation of the building. Carol Culnan’s college roommate Kathleen Cruise got her a job working for Skidmore, Owings, and Merrill (SOM) on the Pennsylvania Avenue Commission, an urban renewal project based on Nathaniel Owings’ proposed mixed-use development of the Avenue. Culnan worked for another firm (DNY&A) under contract with the Washington Metropolitan Area Transit Authority (WMATA) to consult on architectural services for the Metrorail system then under construction (its first line would open in March 1976); she resigned from the firm in early 1975, citing lack of growth and variety in her work in her letter to her supervisors.

For the next nine years the Culnans continued to live in Washington, D.C.. Carol Culnan obtained her license in Washington, D.C., and Maryland, and she practiced architecture independently, working on a mixture of residential and commercial projects, both new build and rehabilitation. In 1984 the couple sold their row house and moved to a rural Virginia community in the Strasburg area, where they continued to practice architecture.

The Culnans were hobbyist antiquarians and collected antique tools, trains, and hurricane lamps. In 1996, Carol and Kenneth joined the Early American Industries Association, a society focused on the history of American tools, crafts, and trades. The couple remained active in the Association for the remainder of their lives. Additionally, Carol raised goats for a time, carded and dyed her own wool, and wove textiles; she also had a lifelong interest in photography. Carol O’Neale Culnan passed away on February 11th, 2025, nearly seven years after Kenneth, who died in April of 2018.