In 1991, she became the first ordained woman to serve as the general secretary for the National Council of Churches of Christ USA.

During her career, she also served as the head of the US office for the World Council of Churches, and later, as director of the Religion Department for the Chataqua Institution.

Eventually, the marriage ended in divorce; according to Campbell, her activism on civil rights and her support of Martin Luther King Jr. led to the breakup.

[8] She was also a member of the board of the National Council of Churches of Christ, USA, and served terms as vice-president and assistant general secretary.

[8] As general secretary, she represented the council at national and international gatherings, including leading a delegation to meet with Pope John Paul II after the NCCC published the New Revised Standard Version of the Bible; the delegation presented the pope with a copy of the Catholic version of the NRSV.

[8] She was the only woman to process among the clergy at the installation of Desmond Tutu as archbishop in the Anglican Church of Southern Africa.

[3] In 2000, Campbell mediated talks between Cuban leader Fidel Castro and US president William Clinton to allow for the return of Elián González to Cuba.