Kate O'Regan was born in Liverpool, England, on September 17th, 1957, into a large family of Irish descent. . With her family, Kate moved to Cape Town, South Africa, when she was seven years old. While living in South Africa, her mother worked as a dentist and her father as a doctor. One of her first memories of exposure to apartheid policy was during the forced removals of local communities in Cape Town in the winter of 1977. Her family assisted people whose homes had been bulldozed by state agencies to move their belongings to local churches where they could take shelter from the winter rains. . Kate originally chose to study journalism, but then shifted to law having been advised by newspaper journalists that it was a useful basic degree for journalism.

Kate O'Regan began her college career at the University of Cape Town. She obtained her Bachelor's in 1978. In 1980, she received her LL.B from the same university, graduating with cum laude honors. Continuing with her educational endeavors, she received an LL.M. from the University of Sydney in 1981 with first-class honors. A few years into her professional career, she went back to school in 1985 to obtain a doctorate in labor law at the London School of Economics. Kate O'Regan graduated from the London School of Economics in 1988 and proceeded on to a long career in the legal field. She later received seven honorary doctorates, including some from the University of KwaZulu-Natal in 2000, the University of Cape Town in 2004, and the London School of Economics and Political Science in 2008.

Kate O'Regan began her legal career as an articled clerk for a large firm of attorneys in 1982 in Johannesburg, South Africa. She spent four years largely working in the fields of labor law and land rights. During her time as an attorney in Johannesburg, she worked on behalf of many trade unions and anti-apartheid organizations. At the time she started work as a lawyer, labor laws had just been amended in South Africa to permit black workers to join trade unions lawfully which heralded extraordinary growth in the black trade union movement during the 1980s. Her labor law work was almost entirely for trade unions representing black workers. Her land work was for communities facing eviction under apartheid land policies. After completing her doctoral studies at the London School of Economics in 1988, she joined the Labor Law Unit at the University of Cape Town. After two years as a researcher, she became a senior lecturer at the University of Cape Town within the faculty of law. She continued to work at the university, heading substantial and impactful research projects. She became one of the founding members of the Law, Race, and Gender research project, as well as the Institute for Development Law.

She was called upon to become an advisor to the African National Congress concerning land claims legislation. Her previous experience as an attorney in Johannesburg made her perfect for the position. Then, she was asked to join the National Manpower Commission on gender equality law. During this same period, she became a trustee of the Legal Resources Trust in South Africa, South Africa’s pre-eminent public interest law firm. Additionally, O'Regan edited a book with Christina Murray on forced removals and the law, No Place to Rest, Forced Removals and the Law in South Africa, 1989 (Oxford University Press). She wrote a series of academic articles on labor law, land law and also edited a digest of labor arbitration decisions. In 1994, she was appointed as a judge to the newly formed Constitutional Court in South Africa alongside Justice Yvonne Mokgoro. They were the only female judges on the Court for the first 13 years after its inception. She was appointed Deputy Chief Justice from February to May 2008. Her term of office on the Court ended in October 2009.

In 2008, she was appointed by the Secretary-General of the United Nations to become the inaugural chairperson of the Internal Justice Council of the United Nations. One of the primary responsibilities that the Council had was identifying suitable individuals for appointment as judges of the UN Dispute and Appeals Tribunals. Her term was four years. Justice O’Regan served as an ad hoc judge of the Supreme Court of Namibia from 2010 - 2016. She also chaired a commission of inquiry into policing in Khayelitsha, Cape Town from 2012 – 2014. After she left the Constitutional Court, O'Regan also continued to teach as an honorary professor at the University of Cape Town and a visiting professor at the University of Oxford. Since 2016, she has been the inaugural Director of the Bonavero Institute of Human Rights at the University of Oxford, which has led her to split her life between Oxford and Cape Town. She has used her knowledge and experience in serving on the boards of many organizations seeking to promote human rights, the rule of law, and democracy in South Africa and beyond such as Corruption Watch, the Equal Education Law Centre, SAFLII NPC, amongst many others. She also serves on the editorial board of many legal publications. Her long career has helped many South Africans and has provided awareness of the injustices people faced under apartheid and other unjust legal systems.

Kate O'Regan has pushed for racial and gender equality in South Africa. She was an early proponent of the principle of racial and gender equality in judicial appointments. She served as legal counsel for black workers and trade unions in South Africa as well as for black South Africans facing evictions under the apartheid laws. Her experience as an attorney acting for black workers and those facing evictions informed her approach to her work as a judge of South Africans on the Constitutional Court of South Africa, to enforce laws that uphold the country’s new democratic system. As a trailblazer in the legal field, Kate O’Regan has shown that a woman can speak out against, and fight unjust laws to seek to ensure that the law is responsive to the needs of ordinary people and that it treats people fairly.