The former Office actor will be playing an accountant for Fat Tony (to be voiced by returning guest star Joe Mantegna), according to Entertainment Weekly.
"He's nervous, and then Fat Tony says that he's got to kill some people and then he's really nervous because he actually wants to do it," executive producer Al Jean said of Carell's character.
"The line between Ivy League MBA and ruthless murderer is a very thin one," he added.
The episode will air in fall 2012.
The Simpsons was renewed for two more seasons by Fox in October.
Jean described the renewal as "a beginning", saying that he hopes the series will go on as long as it can.