Republican John Faso defeated Democrat Zephyr Teachout in a race to replace retiring Congressman Chris Gibson in New York's 19th House District.
The race in a swing district north of New York City now held by retiring Republican Rep. Chris Gibson was marked by a flood of outside money.
Democrats hoped the district would be one of several pick-ups in New York.
Faso returns to elected office 14 years after he left the state Assembly, where he was minority leader. He ran unsuccessfully for state comptroller in 2002 and governor in 2006.
Teachout galvanized liberals with her surprisingly strong 2014 primary challenge to Gov. Andrew Cuomo's re-election bid.
In a victory statement, Faso said, ""Congratulations to Zephyr Teachout on a hard fought race that was closely watched not only by those living in the 19th Congressional District, but by people all over the nation. What we've heard today is that citizens are deeply concerned about our country; that they care about its future; and they want a government that works for them and gets things done. They're tired of gridlock, games and the 24-hour spin cycle and punditry. To those people, I say, I hear you loud and clear. "