CNN said NAACP officials are expected to name Brock as the successor to current Chairman Julian Bond Saturday, ending Bond's tenure as NAACP head. Bond assumed the post in 1998.
Historian Patricia A. Sullivan lauded Bond for his work as the first Southern Poverty Law Center president and for helping found the Student Nonviolent Coordinating Committee.
"I think he's been enormously effective; he's just a thoughtful person with a rich history in civil rights struggles," Sullivan said.
Bond has also been an outspoken supporter of gay rights, appearing at the National Equality March last October.
"I'm fond of saying there's no such thing as saying gay rights or black rights. There's civil rights, and every American deserves civil rights," Bond said at the Washington event.
CNN said Bond, 70, initially planned on vacating his NAACP post in 2008, but remained in the position as the organization celebrated its 100th anniversary in 2009.