(CNN) - Several Democrats, including Sen. John Kerry, offered their endorsement Friday of Rep. Ed Markey in his planned bid to seek the Senate seat Kerry is expected to vacate.
"As Massachusetts' senior senator today and as a colleague of Ed Markey's for 28 years, I'm excited to learn of and support his decision to run for the United States Senate," Kerry wrote in a statement, which also noted he will likely soon hold a job which requires he remain "apolitical."
The support of Kerry, the Democratic Senatorial Campaign Committee - the official body tasked with electing Democrats to the Senate - and the wife of the late Sen. Ted Kennedy will make it challenging for another candidate to enter the field.
Kerry is expected to be confirmed by his Senate colleagues, and Markey told supporters on Thursday that he would run for Kerry's seat in the anticipated special election this spring.
He is the first candidate to have announced publicly he will seek the seat, though other Democrats have indicated their interest. The state's outgoing Republican Sen. Scott Brown, who lost his bid for re-election to a full term, may also throw his hat in the ring.
Markey said he was "humbled and honored" to have Kerry's support and proud to have Vicki Kennedy on his side.
"It is because of Vicki's energy, passion and commitment that Massachusetts and the entire nation are healthier, safer and a place for our children to thrive," he wrote. "I look forward to working with her to promote the health and best interests of the people of Massachusetts."
Some speculated whether Kennedy, whose husband had been elected to eight full terms before his death in 2009, would seek the seat.
The Democratic Senatorial Campaign Committee's head, Sen. Michael Bennet of Colorado, described Markey as "exactly the kind of leader Massachusetts needs in the U.S. Senate."
"At a time when the country needs real leadership that looks out for the middle class, Ed Markey always remembers where he came from and will continue the hard work needed to turn our economy around," Bennet wrote.
Kerry described Markey as "one of the most experienced and capable legislators in the entire Congress and it would be an almost unprecedented occasion for such an accomplished legislator to join the Senate able to hit the ground running on every issue of importance to Massachusetts."
Markey is the longest-serving member of the Massachusetts congressional delegation and the ninth most senior member of the U.S. House.
"Ed's upbringing in Malden and his service as the dean of our delegation means he knows in his heart and in his head just what is important to every corner of our state," Kerry wrote. "He's passionate about the issues that Ted Kennedy and I worked on as a team for decades, whether it's health care or the environment and energy or education."
Kerry first won a seat in the Senate in 1984. That year, Markey was said to have considered running for the upper chamber, but opted out.
Markey is "gutsy and tough, smart and sharp, a workhorse in Congress who has never forgotten where he came from or who sent him to Washington," Kerry wrote.
– CNN's Gregory Wallace contributed to this report