Democrat Mikie Sherrill will flip New Jersey's 11th District, a House seat long held by Republicans, NBC News projects.
The former prosecutor and Navy helicopter pilot's victory over President Donald Trump-backed Republican Jay Webber moves her party one step closer to taking a House majority.
She entered Election Day as a favorite to win the northern New Jersey district, which narrowly supported Trump in 2016. Democrats need a net gain of 23 seats to take control of the chamber.
Sherrill ran as a staunch opponent of the Republican tax plan, which set a $10,000 cap for state and local tax deductions popular in the 11th District. She also backed increased infrastructure spending and pushed to defend and improve the Affordable Care Act, among other issues.
She will replace retiring GOP Rep. Rodney Frelinghuysen.