Cambridge City Councilor Nadeem A. Mazen, the state’s highest-profile Muslim elected official, is planning a run against US Representative Michael E. Capuano in next year’s primary, according to several people familiar with his thinking.
The councilor is plotting a bid to unseat the 10-term Democrat in a congressional district that includes Somerville, Chelsea, Everett, Randolph, half of Cambridge, one-third of Milton, and the majority of Boston.
If Mazen pulls the trigger, it would pit a 33-year-old MIT graduate, entrepreneur, and two-term city councilor against a 65-year-old former Somerville mayor and alderman — two progressives in one of the most Democratic districts in the country.
Capuano has not faced a serious electoral challenge since voters sent him to Washington in 1998.
Mazen has told his colleagues he plans to challenge Capuano, according to several Cambridge City Hall insiders.
“It seems he’s very serious about pursuing a run for Congress,” said state Representative Mike Connolly, a Cambridge Democrat and a friend of Mazen’s who has spoken with him this week.
“He said he’s seriously considering running for Capuano’s Congressional seat,” said Cambridge City Councilor Jan Devereux, a Mazen ally, who talked to him in recent days.
Mazen did not deny that he is eyeing a bid.
“It’s true that I’m beginning to focus on campaign plans for 2018, but until I’ve had the chance to confer with officeholders on one side, and a wide range of allies on the other, I will not be able to comment just yet on any campaign specifics,” he said by telephone Wednesday afternoon.
Paul Trane, a longtime friend and political adviser to Capuano, said the congressman is running for reelection in 2018.
“He’s one of the most anti-Washington-style congressmen in America,” Trane said. “If people look at his opposition to Donald Trump, taking on big banks and the Wall Street CEOs, his opposition to the never-ending wars around the globe, this is a guy who is in touch with his district.”
Unseating any incumbent congressman in a primary is a steep uphill battle.
And Capuano, a pugnacious liberal with a strong local base of support, is largely seen as being politically in line with his district, Massachusetts’ most Democratic and one of the most Democratic congressional districts in the country. (Hillary Clinton beat Donald Trump by more than 70 percentage points in the district, according to the nonpartisan Cook Political Report.)
Capuano, a half-Irish, half-Italian Roman Catholic, was the longtime mayor of Somerville before his congressional victory. In a 10-person field to succeed retiring representative Joe Kennedy II, Capuano racked up big vote totals in Somerville and won overall by a comfortable margin nearly 20 years ago.
A graduate of Dartmouth College and Boston College Law School, Capuano has the brass-knuckle progressivism and Ivy League pedigree that has made him appealing to both the resients of the old ethnic neighborhoods in his district and the new gentrifiers, who have transformed large swaths of Boston, Cambridge, and Somerville in recent years.
In Congress, Capuano has been outspoken on key liberal issues, from opposing the war in Iraq to pressing for federal transportation funding to extend the Green Line.
A close ally of Democratic leader Nancy Pelosi’s during her tenure as House speaker, Capuano helped lead a task force to revamp the way Congress deals with allegations of misconduct.
But Capuano has appeared to drift away from Pelosi’s inner orbit, saying in 2015 that she should go or change her approach, and that House Democrats need leadership who understand “if something that you’re doing is not working, change what you’re doing.”
The Seventh District is demographically diverse. It had a 56 percent minority population in 2012. (Districts are redrawn after each decennial US Census.)
Mazen, whose family moved from Illinois to Andover when he was 5 years old, is the son of an Egyptian-born father and Indiana-born mother. He graduated from Phillips Academy Andover in 2002 and from the Massachusetts Institute of Technology in 2006 with a degree in mechanical engineering.
The founder and chief executive of Nimblebot, a creative agency that makes animated content for technology, nonprofit, education, and government clients, Mazen ran for and won a seat on Cambridge City Council in 2013. He was reelected in 2015 and announced this spring he would not seek reelection.
“I will consider a run for higher office in 2018 or 2020, but I need to focus on our community conversations in the months immediately ahead,” he wrote in a May 4 e-mail to supporters.
In 2015, he cofounded Jetpac — a nonprofit justice, education, and technology policy advocacy center devoted to training more Muslims and other underrepresented minority people to organize and run for public office.
Capuano would start a race with a sizable fund-raising advantage and the ability to raise millions more. Members of Congress have access to powerful party fund-raising apparatuses, giving them the ability to raise huge sums in short period of time.
He had $749,000 in cash on hand at the end of March, federal data show.
Connolly, the state representative, who unseated a longtime incumbent in a Democratic primary last year, said he doesn’t think people should underestimate Mazen.
“He’s transformed the [Cambridge] civic dialogue in some really positive ways,” he said, pointing to affordable housing and science, technology, engineering, and mathematics education as examples.
But, Connolly added, “Congressman Capuano is widely loved and greatly respected.”
Scott Ferson, a key adviser to Congressman Seth Moulton, who beat an incumbent, John F. Tierney, in the 2014 Democratic primary, said: “Far be it from me to discourage anyone from challenging an incumbent.”
But Ferson emphasized beating Capuano would be very tough.
“Seth was able to be successful because he could make the case that it was time for John Tierney to go,” Ferson said. “Mike Capuano is an extremely progressive, attentive congressman. If you are doing your job extremely well, voters are reluctant to choose someone else.”
Joshua Miller can be reached at email@example.com. Follow him on Twitter @jm_bos and subscribe to his weekday e-mail update on politics at bostonglobe.com/politicalhappyhour.