 Justin LongLem (voice) | Lem (voice) |
 Dwayne JohnsonChuck Baker (voice) | Chuck Baker (voice) |
 Jessica BielNeera (voice) | Neera (voice) |
 Seann William ScottSkiff (voice) | Skiff (voice) |
 Gary OldmanGeneral Grawl (voice) | General Grawl (voice) |
 John CleeseProfessor Kipple (voice) | Professor Kipple (voice) |
| FFreddie BenedictEckle (voice) | Eckle (voice) |
 Alan MarriottGlar (voice) | Glar (voice) |
 Mathew HorneSoldier #1 (voice) | Soldier #1 (voice) |
 James CordenSoldier #2 (voice) | Soldier #2 (voice) |
 Alan CummingAlien Mailman (voice) | Alien Mailman (voice) |
 Frank WelkerRipley / Rover (voice) | Ripley / Rover (voice) |
 Jim CummingsLem's Dad (voice) | Lem's Dad (voice) |
 Renée ZellwegerLem's Mom (voice) | Lem's Mom (voice) |
 Candi MiloTeacher (voice) | Teacher (voice) |
 Lewis MacleodAdditional Voices (voice) | Additional Voices (voice) |
 Rupert DegasAdditional Voices / Chief Gorlock (voice) (uncredited) | Additional Voices / Chief Gorlock (voice) (uncredited) |
 Rebecca FrontAdditional Voices (voice) | Additional Voices (voice) |
 Vincent MarzelloAdditional Voices (voice) | Additional Voices (voice) |
 Emma TateAdditional Voices (voice) | Additional Voices (voice) |
 Pete AtkinAdditional Voices (voice) | Additional Voices (voice) |
 Laurence BouvardAdditional Voices (voice) | Additional Voices (voice) |
 Brian BowlesAdditional Voices (voice) | Additional Voices (voice) |
