The United States Senate election of 1978 in Massachusetts was held on November 7, 1978, with the incumbent Republican Senator Edward Brooke being defeated by Democratic Congressman Paul Tsongas.
Primary elections nominating Tsongas and Brooke were held on September 19.
Brooke was dogged throughout the campaign by questions surrounding his 1975 divorce and an ongoing Senate Ethics investigation. Additionally, he faced a competitive primary challenge that may have weakened his standing ahead of the general election. Paul Tsongas's swearing-in or inauguration marked the first time since 1937 that Democrats held both United States Senate seats from Massachusetts.