The 2020 Massachusetts Senate election was held on November 3, 2020 to elect all 40 members of the Massachusetts Senate. Primary elections were held on September 1, 2020. Voters in Massachusetts elected all 40 members of the State Senate to serve two-year terms in the Massachusetts General Court. The election coincided with United States national elections and Massachusetts state elections, including U.S. Senate, U.S. House, U.S. President, and Massachusetts House.

Democrats started the 2019 legislative session with 34 seats. However, after two Republican senators resigned to take other roles, special elections were held in which Democrats flipped both seats, bringing the Democratic caucus to 36 members and leaving Republicans with just 4 senators.

Democrats flipped a third seat on election day with Democrat John Cronin defeating incumbent Republican Dean Tran. Republicans held only 3 seats after the elections.

A special election in the 2nd Hampden and Hampshire district was called after Republican senator Don Humason was elected mayor of Westfield. The election was won by Democratic state representative John Velis, flipping the seat for the Democratic Party.

A special election in the Plymouth and Barnstable district was called after Republican senator Vinny deMacedo resigned to take an academic position. The election was won by Democrat Susan Moran, flipping the seat for the Democratic Party.

Seats where the margin of victory was under 10%:

Italics denote an open seat held by the incumbent party or a seat where the incumbent was defeated by a primary challenger; bold text denotes a gain for a party.