Kennedy released a video announcement on his campaign website Thursday morning before heading out on a campaign swing through the district.
Kennedy started the day greeting commuters at the Newton Center Green Line MBTA Station and was scheduled to make stops later in Milford, Attleboro, Taunton and Westport.
Kennedy, the son of former U.S. Rep. Joseph Kennedy II and a grandson of the late Robert F. Kennedy, recently moved from Cambridge to Brookline, part of the state's newly redrawn 4th Congressional District.
The family has deep ties to the Boston suburb. Brookline is the site of the birthplace of Kennedy's great-uncle, the late President John F. Kennedy.