Russert, 22, a recent Boston College graduate, has been on the radio since 2006 as co-host with pundit James Carville of "60/20 Sports" on XM Satellite Radio.
"Never before in an election cycle has so much attention turned to the youth vote, and Luke will bring a unique perspective to covering it," NBC News President Steve Capus said in a statement.
Russert told MSNBC.com that he realizes some might say it was only his name that got him the job. But he's ready for the challenge and plans to work hard, he said.
"I'm not trying to be my father. He's irreplaceable. I'm simply trying to do something that I think there's a real niche for, that there's a calling for, that has to do with youth, not just in the election but in politics from now on," Russert said.
In a statement, he said he was "humbled and grateful" for the opportunity.
Tim Russert, the host of NBC's "Meet the Press" and Washington bureau chief for the network, died June 13 of a heart attack at 58. He was a longtime and key part of NBC's political coverage, with a profile as high as the anchors he worked alongside.
Luke Russert's role was announced as NBC detailed its plans for the Democratic convention in Denver, Aug. 25-28, and the Republican meeting in St. Paul, Minn., Sept. 1-4.
"NBC Nightly News" anchorman Brian Williams will lead the network's reporting over the four nights for each convention, with MSNBC's Keith Olbermann and Chris Matthews anchoring cable coverage. MSNBC plans to offer 20 hours of daily live convention coverage.
Former "Nightly News" anchorman Tom Brokaw - who has covered every presidential election since 1968, NBC noted - will do reporting and analysis on both NBC and MSNBC.
"Meet the Press," with Brokaw as moderator, will air from Denver on Sunday, Aug. 24, and from St. Paul on Sunday, Aug. 31.
CNBC, Telemundo, MSNBC.com and NBC Mobile also will be reporting on both conventions.
