His work as a legislator has informed his research interests, and he has subsequently published on the legislative process (specifically the Backbench Business Committee), conducted empirical research 'The Reality of the Constitution'. Highlights of his legislative scrutiny included work on the Companies Bill; highlighting the problems with the Legislative and Regulatory Reform Bill; the Constitutional Reform and Governance Bill; and various Criminal Justice Bills. Howarth also was successively Shadow Minister for Local Government (2005-6); Shadow Minister for Energy (2006-7); Shadow Solicitor General (2007-9); and Shadow Secretary of State for Justice (2009–10). He served on the Constitutional Affairs, Justice and Environmental Audit Select Committees.