Mass. Gen. Laws ch. 43 § 50
The legislative powers of the city shall be vested in a city council, consisting of nine persons, elected at large by and from the qualified voters of the city. One of its members shall be elected by the council annually as its president. At the first election held in a city after its adoption of Plan A, except as otherwise provided in this section, the five candidates receiving the largest number of votes shall hold office for two years, and the four receiving the next largest number of votes shall hold office for one year. Thereafter, as these terms expire, there shall be elected at each annual city election a sufficient number of members to fill the vacancies created by the expiration of said terms, each member so elected to serve for two years.
If the plan adopted provides for elections to be held biennially, at the first regular municipal election held under the provisions of such plan and at each biennial election thereafter, there shall be elected nine members of the city council to serve for two years from the first day of January following their election and until their successors are qualified.
Mass. Gen. Laws ch. 43, § 50