Before entering parliament Baroness Armstrong spent time overseas as a VSO volunteer. Returning to Britain, she turned to Social and Community work in Sunderland and Newcastle upon Tyne. Building on these experiences she became a lecturer in Youth and Community Work at Sunderland Polytechnic (now Sunderland University).
As a Member of Parliament, Hilary served as an opposition frontbench spokesperson on Education (1988–1992). In 1992 she was made Parliamentary Private Secretary (PPS) to opposition leader, the late John Smith MP. She was appointed to the Treasury Affairs Team in 1994 and in 1995 was made Opposition spokesperson on the Environment and London, with responsibility for Local Government.
In 1997 she was appointed Minister of State at the Department of Environment, Transport and the Regions with responsibility for Local Government and Housing. Here she had special responsibility for Social Exclusion and oversaw the creation of the government’s Social Exclusion Unit. In 1999 Hilary was made a member of the Privy Council.
In 2001 Hilary was promoted to the Cabinet and appointed Parliamentary Secretary to the Treasury and Government Chief Whip. She was re–appointed as Government Chief Whip in 2005.
In May 2006 Hilary was appointed to the post of Chancellor of the Duchy of Lancaster, Minister for the Cabinet Office and Social Exclusion which included co-ordinating a cross-government effort to breakdown the barriers for those excluded from society and to expand the ways in which government works with the voluntary sector.
In 2009, Hilary announced her intention to stand down at the 2010 General Election.
And in 2010, she was created a life peer as Baroness Armstrong of Hill Top, of Crook in the County of Durham, and was introduced in the House of Lords on 6 July 2010 Hilary Armstrong published "Reaching Out - an Action Plan to combat Social Exclusion" in September 2006.