Mass. Gen. Laws ch. 53 § 14
If a candidate nominated for a state, city or town office dies before the day of election, or withdraws his name from nomination, or is found ineligible, the vacancy, except for city offices where city charters provide otherwise, may be filled by the same political party or persons who made the original nomination, and in the same manner; or, if the time is insufficient therefor, the vacancy may be filled, if the nomination was made by a convention or caucus, in such manner as the convention or caucus may have prescribed, or, if no such provision has been made, by a regularly elected general or executive committee representing the political party or persons who held such convention or caucus. In the event of the death, withdrawal, ineligibility or disqualification of a candidate for governor or lieutenant governor who has been nominated by election nomination papers, except disqualification for insufficient signatures, the vacancy shall be filled by majority vote of the committee of five members whose names were placed upon said papers for the purpose before the signatures of voters were obtained thereon. In the event of the withdrawal, death or ineligibility of any candidate of a political party nominated by direct nomination for any office, the vacancy may be filled by a regularly elected general or executive committee representing the election district in which such vacancy occurs, or, if no such committee exists by the members of the town committee in any town comprising such district, by the members of the ward committee or committees in the ward or wards comprising such district if within the limits of a single city, or by delegates chosen as hereinafter provided by and from the members of the ward and town committees in the wards and towns comprising such district if within the limits of more than one municipality, at a meeting to be called by such a member or delegate, as the case may be, designated by the chairman of the state committee, and such member or delegate shall preside until a chairman of such meeting is elected. Each ward and town committee in the wards and towns compromising such a district within the limits of more than one municipality shall, as occasions arise, choose from its members delegates to fill vacancies as hereinbefore provided, in such manner as it may determine by its rules and regulations, to a number not exceeding one for each five hundred votes, or fraction thereof, cast in its ward or town for the candidate of the party for governor at the last state election, and shall forthwith notify the state secretary of the delegates so chosen. Notwithstanding any of the foregoing, when a vacancy occurs, by reason of withdrawal, death or ineligibility in a district comprised of portions of wards of a city or not all precincts of a town, then each ward and town committee which includes the precincts which are part of the district shall choose delegates as hereinabove provided to fill vacancies in such number not exceeding one for each five hundred votes or fractions thereof cast in that portion of the ward or town included in the district for the candidate of that party for governor at the last state election, provided further that said delegate so chosen shall reside in the district where the vacancy occurs. In cities and towns where candidates are nominated by nomination papers, such papers may contain the names of members of a committee of not more than five registered voters who may fill any vacancy caused by the death or physical disability of the candidate whose name appears upon such nomination paper. If a vacancy is caused by withdrawal, certificates of nomination made otherwise than in the original manner shall be filed within seventy-two week day hours in the case of state offices, or within forty-eight week day hours in the case of city or town offices, succeeding five o'clock in the afternoon of the last day for filing withdrawals. They shall be open to objections in the same manner, so far as practicable, as other certificates of nomination. No vacancy caused by withdrawal shall be filled before the withdrawal has been filed.
Mass. Gen. Laws ch. 53, § 14