Mills worked in legal publishing, where she joined the
National Society of Operative Printers and Assistants. She was elected as
Mother of the Chapel, representing other trade unionists at her workplace, before taking a full-time post with the
Society of Graphical and Allied Trades. In 1985, she moved to work for the
National Union of Public Employees (NUPE) as an area officer in the London Division, before being promoted to a national officer post responsible for equalities work within the union. In 1993, NUPE merged with two other unions to form
Unison, and Mills became its director of equal opportunities. Two years later, she was elected to the
General Council of the Trades Union Congress (TUC), also serving on its executive committee from 2000, chairing its race committee and sitting on its women's committee. She was elected as
President of the Trades Union Congress from 2005 to 2006. Mills also served on the
Commission for Racial Equality. She has been active in the
Labour Party over many years and is a National Executive Member of
BAME Labour. ==Honours==