WAKEFIELD — Come January, the North Shore will  be represented in Congress by someone other than John Tierney.

And there’s a chance Main Street Republican Richard Tisei will be that man.

The political current is changing from Wakefield to Amesbury, from Bedford to Lynn. Tierney was defeated in yesterday’s Democratic primary for the 6th Congressional District seat by Seth Moulton, an Iraq War veteran from Marblehead who also happens to be a Harvard graduate and a successful businessman. Tierney, who served 18 years in Congress, was skewered in a Moulton TV ad in which Tierney’s record of passing just one bill in his time in office was highlighted.

Tisei, who ran unopposed in the Republican primary, barely lost to Tierney two years ago, showing the longtime incumbent was vulnerable. Four Democrats, including Moulton, ran against Tierney yesterday.

Tisei, who used to represent Wakefield on Beacon Hill, said, “I want to congratulate Seth for his win tonight. The real fight to change the direction of our country begins now. Seth himself has said repeatedly in Congress he would vote the same as John Tierney. That means Seth Mouton will rubberstamp the failed direction Washington is taking our country.

“The choice in this election is clear. Who will be the most effective advocate for change and progress in Washington? I’m the only candidate who has represented and fought for working families. From expanding healthcare, to welfare, and education reform, I am the only candidate in this race with a record of results for the North Shore.

“This District and our state have suffered in Washington from a lack of leadership. Our issues have been on the back burner for too long and need to be placed front and center in Washington. I believe that I will be able to accomplish great things for this District as a member of the majority party.”

Moulton thanked his supporters at a victory party held at the Veterans of Foreign Wars post in Salem.

“Our win tonight says two things,” said Moulton. “First, that we are fed up with the gridlock in Washington. And second, that voters want to keep this seat blue.”

Tierney gave a short concession speech last night and thanked his family for the support they have given him over the years.

“I’m proud of the work that we’ve done in Congress,” Tierney said. “This was just an amazing 18 years.”

During much of the primary Tierney had focused his attention on Tisei.

Then, late in the primary, Tierney launched a campaign ad linking Moulton to Republicans who support gun rights and oppose abortion rights. The ad focused on money the Moulton campaign received from the White Mountain PAC, which is affiliated with former U.S. Sen. Judd Gregg, a New Hampshire Republican.

Moulton said the ad showed that Tierney believed he was a serious challenger.

Moulton has argued he would have a stronger chance of holding off Tisei, the former Wakefield state Senator who lost to Tierney by less than 1 percent of the vote in the 2012 election. Tierney had responded by saying he had beaten Tisei.

Immigration attorney Marisa DeFranco and two other Democrats, John Gutta and John Patrick Devine, also were on the primary ballot.

It was the second tough campaign for Tierney. In 2012, he was dogged by questions about what he knew of an illegal offshore gambling ring involving his wife’s family.

Moulton described himself in a campaign ad as a “progressive Democrat who opposed the war in Iraq.”

“But I also was a Marine serving my country,” Moulton said. “So I went, led my platoon and always ate last after my men.”

During the campaign, Moulton expressed his opposition to another ground war in Iraq as President Barack Obama considers the nation’s options for fighting back against Islamic State militants.

Moulton also backs abortion and gay rights, tighter restrictions on gun ownership and comprehensive immigration reform. About 8 percent of the district’s population served in the military, and about 15 percent are age 64 or older.

During the primary, Moulton suggested that Tierney’s victory two years ago was due in part to the political coattails of Obama and consumer advocate Elizabeth Warren, who were on the ballot and helped draw Democrats to the polls. Warren won a U.S. Senate seat against Republican Scott Brown.

Tierney had rejected Moulton’s suggestion, arguing that he had the issues on his side.

The general election could be equally hard fought.

Republicans see the Sixth Congressional District at their best chance to pick up a seat in Massachusetts.

Tisei has already been the beneficiary of a $350,000 ad buy from the conservative U.S. Chamber of Commerce earlier in the year. The 30-second ad, which ran on TV and online in May, portrayed Tisei as “an independent voice for Massachusetts.”

— The Associated Press contributed to this report.