Former congressman Joseph P. Kennedy II (pictured) of Massachusetts said on Sunday that he would not run for the U.S. Senate seat vacated by his uncle, Sen. Edward M. Kennedy, who died of brain cancer last month. The announcement is expected to break the field of Democratic contenders wide open and lead to a hotly contested race.

Kennedy, the 56-year-old eldest son of Robert F. Kennedy, decided to remain in the private sector as head of an energy firm after speaking with his wife and twin sons, according to the Boston Globe. Other members of his family, including his mother, Ethel, reportedly encouraged him to run.

“My father called politics an honorable profession, and I have profound respect for those who choose to advance the causes of social and economic justice in elective office,’’ Kennedy said in a statement, reported the Boston Globe. “After much consideration, I have decided that the best way for me to contribute to those causes is by continuing my work at Citizens Energy Corporation.’’

The decision likely will propel more senior Democrats into the race who otherwise would have deferred to Kennedy. Thus far, the only Democrat to declare her candidacy officially is state attorney general Martha Coakley.

Canton selectman Bob Burr, a Republican, declared on Sunday that he would run.

The primary will be held on December 8. The special election is scheduled for January 19.