The new panel combines the legal spends of government bodies the Welsh Assembly Government, Countryside Council for Wales, Sports Council for Wales, Arts Council of Wales, Care Council for Wales, Royal Commission on the Ancient and Historical Monuments of Wales and the Office for National Statistics.
The panel's legal spend is not yet confirmed, but is expected to top £8m over the contract.
The panel is split into sub-groups covering commercial law, corporate finance, litigation, employment and environmental law.
An overarching panel has also been created including all six firms appointed under the subject areas together with two others.
Members of this panel will be invited to tender through mini-competitions for large scale cross-practice projects.
Firms appointed to subject area panels are Bristol-based Bevan Brittan, Nottingham-based Browne Jacobson, Eversheds, Cardiff-based Geldards, Cardiff-based Hugh James and Cardiff-based Morgan Cole.
Also appointed to the wider panel are Bristol-based Ashfords and London firm Beachcroft.
Panel members are appointed for a period of four years, and the appointments are with immediate effect.
The groups in full are: Property and Commercial:Bevan Brittan, Browne Jacobson, Eversheds, Geldards, Hugh James. Corporate Finance: Geldards, Hugh James. Environmental: Browne Jacobson, Eversheds. Employment: Eversheds, Geldards, Morgan Cole Litigation: Eversheds, Geldards, Hugh James. Overarching Panel Members: Ashfords, Beachcroft.