NEWTON, Mass. – Joseph Kennedy III officially launched his campaign for the U.S. House on Thursday, embracing his family’s legacy in Massachusetts while also acknowledging that name alone will not assure him electoral success.

“You’ve got to earn it,” Kennedy told reporters after greeting commuters at a train station in Newton, the first of several stops the Democrat planned to make in the reconfigured 4th Congressional District.

“You’ve got to go out every day and talk to people, listen to their concerns, shake more hands, knock on more doors, take more phone calls.”

Kennedy, 31, is seeking the seat held by the retiring U.S. Rep. Barney Frank.

Kennedy’s official announcement was largely a foregone conclusion after he said last month that he was forming an exploratory committee to run for the seat.

The redheaded son of former U.S. Rep. Joseph P. Kennedy II and grandson of the late Robert F. Kennedy later resigned his job as a prosecutor in Middlesex County and moved from Cambridge, outside the 4th district, to Brookline, within the district.

He has already been endorsed by two major labor unions and a recent poll showed him with a commanding early lead over Republican Sean Bielat, who lost to Frank two years ago and is running again.