Both actors will make their debut in the zombie drama's midseason premiere, titled 'Nebraska'.
Cadillac Records actor Munoz will play a character named Tony who joins with Rick (Andrew Lincoln) and the other survivors, according to Shock Till You Drop.
James will play an unspecified role. He is best known for his roles on HBO's True Blood and short-lived FX drama Terriers.
It was recently reported that Michonne - a popular character from the Walking Dead comic - was to debut on the show, with rumours suggesting that True Blood's Rutina Wesley had been cast in the role.
However, executive producer Robert Kirkman later announced that the character's appearance was "not confirmed".
"I can say that's definitely a character we want to work into the show at some point in the future," he said. "Whether that happens this season, I don't really know."
The Walking Dead returns to AMC in the US on February 12. The show resumes on FX in the UK on February 17.
> The Walking Dead's Jon Bernthal wanted for TNT L.A. Noir pilot
> Frank Darabont reveals aborted Walking Dead premiere plans
Watch a preview for the return of The Walking Dead below: