U.S. media outlets including Little Rock, Arkansas, TV station KATV reported Jaylen Smith won a runoff election on Tuesday to become the mayor of Earle.
Jaylen Smith, was elected mayor, winning 235 votes to Nemi Matthews' 183, according to complete but unofficial results.
The university student graduated from Earle High School in May.
He told KATV that his involvement with the school's student government inspired him to run for office.
"People are crying out for change, and I want to be the change to move Earle forward," he said.
Smith also admitted that his age made it difficult for some voters to take him seriously.
"But I've always told people you have to start somewhere in life," he said.
Smith campaigned on improving public safety and bringing new businesses, including a grocery store, to the city of about 1,800 people 25 miles (40 kilometers) northwest of Memphis, Tennessee.
Cymone Poole says she voted for Smith. She told KATV that Smith impressed her, despite his youth.
"It's just in him. You know, the way he walks, he talks, he dressed. You know, it's just in him to lead."
He's among the youngest mayors elected in the United States and would be the youngest member of the African American Mayors Association.
Phyllis Dickerson, chief executive officer of the association, told the Arkansas Democrat-Gazette that the association's current youngest member is Cleveland Mayor Justin Bibb, who is 35.
Smith is among a handful of people elected mayor before turning 20, including Michael Sessions, who was elected mayor of Hillsdale, Michigan, in 2005 when he was 18; and John Tyler Hammons, who was elected mayor of Muskogee, Oklahoma, in 2008 when he was 19.
According to KATV, Smith is set to be sworn in on New Year's Day, and serve a four-year term.