Five years later she achieved ministerial office as Under-Secretary of State at the Scottish Office, and went on to become Minister of Pensions and National Insurance (Social Security from 1966) in Harold Wilson’s Labour Government in 1964. While in post she abolished the means-tested national assistance scheme, so loathed by the left, and replaced it in 1966 with Supplementary Benefit that operated until 1988.

She was a member of Labour’s National Executive from 1948-60 and party Chair from 1956-7. In July 196,7 she resigned office in protest at the government's refusal to increase children's allowances. In the House of Commons, she was Chairman of Select Committee on Overseas Aid in 1969-70 but retired from parliament at the general election in that year. She was also voted Scotswoman of the year in 1970.

In 1970-71, she was appointed Lord High Commissioner to the General Assembly of the Church of Scotland, the first woman to hold the office.