The highest decision-making body of the Regional Council of Häme is the assembly with its 54 members. At the beginning of each legislative period of the local government board, the municipal council that is formed by the representatives elected by the member municipalities elects the assembly for the next legislative period of the local government board. The number of the representatives of each municipality varies from two to thirteen depending on the population of the municipality. The members and the deputy members of the assembly must be representatives that have been elected by the citizens of the member municipalities in the municipal election. The assembly differs from all other organisations on the regional level in that its members are chosen directly by the citizens of the member municipalities.
The assembly of the regional council is responsible for creating a regional will and the definition of policy both in regard to regional development and planning as well as protection of interests. A central responsibility of the assembly is approving the provincial plan and programme as well as the regional construction plan of the Regional Council of Häme. In addition, the assembly is responsible for the activities and the finances of the Regional Council. The assembly elects the executive director, the managing board, the board of inspection and the board of directors for the Summer University.
The assembly convenes two or three times every year.