The daughter of a school teacher mother and an accountant father, after leaving school McEwen went on to work in clerical and administrative positions within both the private and public sectors.

During the 1980s, McEwen undertook tertiary study as a mature age entry student at the University of Adelaide, graduating in 1987 with a Bachelor of Arts degree with majors in politics and English literature.

In 2003, McEwen was awarded the Centenary Medal for her services to trade unionism as the Secretary of the ASU SA+NT.

During her time in Federal Parliament, McEwen was particularly active on issues regarding workplace relations, higher education, Australia's indigenous population, and veterans' affairs.

Until the 2016 election, McEwen was the duty senator for the federal electorates of Sturt and Barker in South Australia.