Jealous told The Associated Press recently that a broader coalition is needed to fight the civil rights battles of the 21st century.
"Last century we needed lawyers; this century we need big, broad coalitions," he said. "When extremists decide to attack all our communities, they must hope that there will be infighting. But we have stood all for one and one for all. That is how we will win."
An NAACP spokesman said Jealous was not available for an interview until a formal announcement on Monday.
Jealous began his career as a community organizer in Harlem with the NAACP Legal Defense Fund. He was suspended from Columbia University in New York City after organizing student protests and went on to work as a reporter for the Jackson Advocate newspaper in Mississippi.
Jealous has led the NAACP to advocate against "stop-and-frisk" police tactics and stand-your-ground laws following the death of Florida teenager Trayvon Martin. He has also fought to abolish the death penalty at the state level.
NAACP Chairman Roslyn Brock accepted Jealous' resignation in the past week. She said the group would continue its fight to restore part of the Voting Rights Act that was recently struck down by the Supreme Court, as well as work to boost its civic engagement efforts and ensure that black Americans are able to obtain health insurance under the nation's health care overhaul.
Brock thanked Jealous for his service.
"Under his leadership, the NAACP has built a highly competent staff that will carry our mission forward and meet the civil rights challenges of the 21st century," she said. "Our board, staff and volunteer leaders throughout the country deeply appreciate his sacrifice and will continue to implement our game-changing goals for the next half century."