The highest decision-making body of HSL is the General Meeting to which each member municipality elects its representatives. The General Meeting convenes at least twice a year. The General Meeting approves the financial statements of the joint local authority not later than by the end of May annually and approves the budget and financial plan by the end of November annually.
The voting rights are divided according to the population of the member municipalities. One municipality can hold a maximum of 50 per cent of the votes. In 2018, Helsinki has 49.7 per cent of the votes, Espoo 21.4 per cent, Vantaa 17.2 per cent, Kirkkonummi 3.1 per cent, Tuusula 3.0 per cent, Kerava 3.0 per cent, Sipoo 1.6 per cent, Kauniainen 0.7 and Siuntio 0.5 per cent.
The Executive Board of HSL protects the interests of the joint local authority, supervises its management and establishes its operational principles. The Executive Board also approves the fares and tariffs, determines the quantity and quality of public transport services provided, makes decisions on the services to be procured and approves service contracts.
The Chairperson of the Executive Board, its Deputy Chairperson as well as Board members are elected by the General Meeting. The term of office of the Executive Board is the municipal electoral period, i.e. four years.
The Executive Board of HSL consists of 14 members: Chairperson, Deputy Chairperson and 12 other members. They all have personal deputies.
In 2017–2021, Helsinki has seven members and six deputies, Espoo has three members and two deputies, Vantaa has three members and three deputies, Kirkkonummi has one member, and Kerava, Sipoo and Tuusula have one deputy. Kauniainen and Siuntio have appointed an expert representative. The deputies always have the right of attendance and right of speech if they are the sole representatives of their municipalities in the Board meetings. Also expert representatives have the right of attendance and right of speech in the Board meetings.
The Audit Committee consists of a Chairperson, Deputy Chairperson and three other members elected by the General Meeting. Each member has a personal deputy. The tasks and duties of the Committee are set out in the Local Government Act and determined in the administrative rules of HSL.