Hart was born and raised in Gowerton, Swansea where she attended Gowerton Girls' Grammar School. She especially enjoyed English and Music and became a member of the National Youth Orchestra of Wales. Today Edwina lives in Gowerton with her family; she has one daughter.
Hart has worked in banking, where she became active in the trade union movement. As a result of this work she was elected as the first female president of the Banking, Insurance and Finance Union, serving from 1992–1994. She also served as Chair of the Wales TUC (as did her husband, Bob Hart, in another year). Hart later received an MBE for Trade Union services. In 1998 Edwina also served as a member of the Broadcasting Council for Wales and sat on the board of the Wales Millennium Centre. She also sat on the Employment Appeals Tribunal, was a member of the South West Wales Economic Forum and a director of Chwarae Teg. Edwina is a member of T&GWU and Community as well as a life member of Amicus.
Hart was elected to the First Assembly with 35.4% of the vote in 1999 for the constituency of Gower. She became the Assembly's first Finance Secretary. In 2000, this was changed to include responsibility for local government and she became Minister for Finance and Local Government.
She was re-elected to the Second Assembly in 2003, increasing her majority to 5688 (+8.2%) with 43.60% of the vote. After the election she took on the newly created Social Justice portfolio and became the Assembly's first ever Minister for Social Justice and Regeneration Minister, whose responsibilities include community safety, youth justice, police relations, fire service, alcohol and drug abuse, social economy, anti-poverty, housing, social housing, the voluntary sector, issues relating to asylum and immigration, liaison for armed forces in Wales, veterans, regeneration of communities, and development.
In 2004, in her role as Minister for Social Justice, Hart commissioned an independent report on charity All Wales Ethnic Minority Association's projects. The report stated no new projects should be funded until AWEMA demonstrated improved project and performance management, and that as a result AWEMA should be graded "high risk" by as a publicly funded institute.
She was once again re-elected to the Third Assembly in May 2007 with a reduced majority of 1192 (34.2% of the vote) and was appointed Minister for Health and Social Services (31 May 2007). She retained this position when the coalition government of Labour and Plaid Cymru was announced on 19 July.
In October 2009, Hart announced that she would stand for leadership of the Labour party in Wales after Rhodri Morgan's retirement, on a commitment to carry on the "Clear Red Water" of Rhodri Morgan. Whilst she secured backing from a number of Unions and prominent figures such as Finance Minister Andrew Davies, Hart finished second in the Leadership contest. She retained her position as Minister for Health in the cabinet appointed by First Minister Carwyn Jones.
In September 2010, Hart was accused by Welsh Liberal Democrats of withholding a consultants' report that criticised the leadership of the NHS by the Welsh Government.
Hart was nominated the best-dressed Welsh politician of the year. According to Peter Black AM, Hart beat some other competition to take this prize including Welsh Secretary Peter Hain. Hart also controversially ruled out a review of NHS spending in Wales on 12 November 2009, declining Liberal Democrat Kirsty Williams request to review how £1 billion has been spent on NHS services, following evidence to the Welsh Assembly's Finance Committee that claimed £1 billion was 'wasted' in the Welsh NHS each year.