The race was one of 11 gubernatorial elections held Tuesday, nine of which involved incumbents.
North Carolina's race was one of just three in which experts expected a close race, though most said the odds favored Cooper, who in 2017 unseated then-Republican Gov. Pat McCrory in a race so close it took nearly a month and multiple recounts to call.
Republican governors were expected to hold onto their seats in Indiana, New Hampshire, North Dakota, Utah, Vermont and West Virginia.
In West Virginia, Democratic challenger Ben Salango conceded the race to Republican Gov. Jim Justice, who was elected in 2016 as a Democrat.
Experts predicted a tight race in Montana, where Democrat Mike Cooney and Republican Greg Gianforte battled to replace Democratic Gov. Steve Bullock, who has been the state's governor since 2013 but can't seek a third term.
Gianforte has served as the state's sole House representative since 2017 and made national news during that year's special election after assaulting a reporter.
In Missouri, Republican incumbent Mike Parson faced a tight race against Democrat Nicole Galloway, but ended up retaining his governorship with 57.1% of the vote, the office of Missouri Secretary of State John Ashcroft said. Galloway earned 40% of the ballots, it said, adding that all 3,692 precincts have reported.
Parson was diagnosed with COVID-19 in September, but that did not slow his campaign against Galloway, who sought to become the state's first female governor.
The office of the state's secretary said Inslee earned 59.3% of the vote to Culp's 40.41%.
"We are still facing great challenges, but I have never been more optimistic about our capacity to meet them," Inslee, who was first elected governor in 2012, said in a statement. "Our victory tonight is more than just a reflection of our successful past -- this is about a mandate for governing into the future."