With most of the precincts reporting, Runyan had 50 percent of the vote to 48 percent for Adler, a freshman Democrat in what had been a Republican district in South Jersey, The Star-Ledger of Newark reported.
Republicans had hopes of picking up two more seats in the state, but Rush Holt, a physicist representing a district that includes part of Trenton and suburban areas north of the capital, and Frank Pallone Jr., who has been in the house since 1988, easily won re-election.
Runyan, a Michigan native, played in the NFL for more than a decade, mostly for the Philadelphia Eagles. This was his first run for political office.
Adler, a graduate of Harvard Law School, served 17 years in the state Senate before his election to Congress in 2008.
Adler's defeat leaves the Democrats with seven House seats in New Jersey to six for the Republicans. New Jersey has off-year state elections and neither of the U.S. senators were up for election, so the House races were at the top of the ballot.