Before becoming the ED at the ACLU of Virginia, Claire was the principal of CG2 Consulting - a consulting firm that specialized in providing strategic governance, management and public policy advice to colleges and other not-for-profit organizations and trade associations. Her skill in bringing diverse people together to address issues of common concern was highlighted in "The Facilitator," a cover story in the Metro Business magazine of the Richmond Times Dispatch.

While running her consulting firm, Claire was active in the National Association of Women Business Owners (NAWBO), serving on the boards of the Richmond chapter and the National organization. She was recognized by NAWBO as its chapter public policy advocate of the year in 2004 and by the U.S. Small Business Administration as the 2003 Virginia Women in Business Advocate of the Year. In 2007, she was appointed by the Governor to the Virginia Small Business Advisory Board.

As Chief Deputy Attorney General of Virginia, Claire supervised the legal work, shared responsibility for the budget and day-to-day operations and guided the legislative activities of the Office of the Attorney General -- a public law firm with an annual budget then exceeding $15 million and over 250 employees. As a Deputy, she served as the Office's "hiring partner" supervising attorney recruitment and hiring and managed the legal representation of state agencies in the Human Resources, Natural Resources and Higher Education Secretariats. She also argued cases in the United States Supreme Court and the Supreme Court of Virginia, led a nation-wide recall of Ford E350 ambulances, and helped shut down a rayon manufacturing plant that was polluting ground, air, and water in Northwest Virginia. In Wilder v. VHA, she shared oral argument time in the U.S. Supreme Court with now Chief Justice John Roberts and was opposed by former Solicitor General Walter Dellinger in his first Supreme Court appearance.

Claire started her career as a federal civil rights lawyer and then served as assistant university counsel and assistant secretary of the corporation at Princeton University, where she staffed several committees of the Board of Trustees and lectured in the politics department.

Later, as assistant general counsel and associate director of the Office of Federal Regulatory Affairs at the American Council on Education, Claire managed a variety of federal regulatory issues affecting higher education including affirmative action, gender equity in athletics, unrelated business income tax, human subject research, small producer hazardous waste and reasonable accommodation of disabled students, faculty, and staff.

In private practice at Hogan & Hartson (now Hogan Lovells), Claire helped build the firm's higher education practice representing and advising public and private colleges and universities on accreditation matters, faculty tenure issues, academic freedom, governance issues, health care provider questions, environmental issues, export/import problems, building design and construction problems, government contracts and audit issues, Title IX compliance and student personnel matters, among others.

Claire was a trustee of Chatham College (now Chatham University) from 1981-87 and served as the College's interim president during the 1982-83 school year -- a year in which Chatham overcame a serious budget deficit, reduced the size of its faculty and staff and implemented a new core curriculum. She is a former director of the National Association of College and University Attorneys (NACUA) and was honored as one of the first two "Fellows" of the Association in recognition of her contributions to higher education law. In 2002, the Governor of Virginia appointed Ms. Gastañaga to a four-year term as one of Virginia's Commissioners on the Education Commission of the States.

As a volunteer, Claire currently serves on the Boards of the Diversity Conference of the Virginia State Bar, the Metropolitan Richmond Women's Bar Association and Legislative Reform for the Intellectually and Developmentally Disabled. In the past, she has served on the boards of the Girl Scouts of the Commonwealth Council, the National Association of Women Business Owners (local and national), the Richmond Gay Community Foundation (now Diversity Richmond), the Richmond Metropolitan Convention and Visitors Bureau, the Virginia Foundation for Women, the Poe Museum, Chatham University (where at age 32 she also served as interim president), and the National Association of College and University Attorneys, which recognized her as one of its first two Fellows in Higher Education Law. She also served on the Virginia State Advisory Committee to the U.S. Commission on Civil Rights from 2015-2019.

Claire has been recognized twice for her advocacy on behalf of the LGBTQ community, once in 2013 by the Serpentine Society at the University of Virginia which honored her with the Bernard D. Mayes award and a second time in 2015 when Equality Virginia named her as one of its OUTstanding Virginians for her decades of advocacy work including serving as EV's interim director and campaign manager for The Commonwealth Coalition 2006 campaign against Virginia's anti-marriage equality amendment.