John Boehner beat back a conservative challenge to win a third term as House speaker on Tuesday, as he joined Sen. Mitch McConnell in presiding over the first Republican-controlled Congress in nearly a decade. 

Boehner, at the start of the 114th Congress, now leads the biggest GOP House majority in nearly 70 years. McConnell, after his party picked up nine seats in the midterms, leads a 54-seat majority in the Senate. Boehner, in brief remarks before taking the oath, put jobs and the economy at the center of their agenda. 

"Far too [many] Americans remain out of work. Too many are working harder only to lose ground to stagnant wages and rising costs. We can do better," Boehner said. "We can build an economy that furthers better-paying jobs, more growth and more opportunity for the nation's middle class. This is our vital task." 

Earlier Tuesday, McConnell formally assumed the post of Senate majority leader, taking over for Harry Reid, who could not attend due to an injury he sustained while exercising at home last week. 

The election for House speaker aired lingering divisions in the GOP. Three conservative lawmakers -- Reps. Louie Gohmert, R-Texas; Ted Yoho, R-Fla.; and Daniel Webster, R-Fla. -- were put forward as challengers; a total of 25 Republicans voted for candidates other than Boehner or voted present. Democrats mostly voted for California Rep. Nancy Pelosi, the minority leader. 

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But Boehner garnered 216 votes, slightly more than the majority needed to clinch the speakership. 

With the GOP leadership team in place, Republicans are poised to charge ahead with an agenda focusing on jobs, ObamaCare and other issues -- while serving as a stiff check on President Obama's policies every step of his final two years in office. 

The first move by majority Republicans is to push legislation, being introduced in both chambers on Tuesday, to approve the controversial Keystone pipeline. 

The House plans a vote on Friday. 

Such a bill passed the House but died in a Democratic-led filibuster in the Senate late last year. Now, Republicans appear to have more than enough votes to clear it through the Senate as well, given the Republican pickup of nine seats in the elections. 

The White House on Tuesday, though, threatened to veto the measure, setting up a looming showdown with the new Congress. "If this bill passes this Congress, the president wouldn't sign" it, White House spokesman Josh Earnest said Tuesday, saying legislation shouldn't undermine the review process underway at the State Department or circumvent a pending lawsuit in Nebraska over its route. 

But Republicans stand ready to cast the measure as a bipartisan jobs bill of the type that should become law. 

"There's a lot we can get done together if the president puts his famous pen to use signing bills rather than vetoing legislation his liberal allies don't like," McConnell said late last year. 

The challenge Tuesday to Boehner's leadership post was driven by complaints that Boehner has strayed from conservative roots. Conservatives complain he has leaned on Democrats to help pass key legislation, including a budget package approved before the winter recess. 

Virginia Rep. Dave Brat, who defeated former Majority Leader Eric Cantor in a primary last summer, said the Republican leadership has "strayed from its own principles of free market, limited government, constitutional conservatism." 

Two years ago, Boehner faced similar criticism, and sweated out his election to a second term. His hand was considerably stronger this year after the Republicans' sweeping electoral triumph. The party will hold 246 House seats in the new Congress, to 188 for the Democrats. 

Seventy-one new members were entering Congress on Tuesday, most of them Republicans. On Monday, Boehner outlined the early agenda, which would focus on jobs and the economy. 

Aside from the Keystone bill, his office said their priorities would include: a bill exempting veterans with military or VA health plans from being counted toward employers' ObamaCare threshold, after which they must provide health care; and a bill to restore the traditional 40-hour work week, amid concerns that a quirk in ObamaCare has businesses keeping hours down to 30 per week to avoid a penalty. The White House on Tuesday also threatened to veto the latter bill. 

Fox News' Chad Pergram and The Associated Press contributed to this report.