After Six Feet Under ended in 2005, Hall took on a much darker and more sinister role as the serial killer protagonist Dexter. Dexter is a sociopath who disciplines himself to kill only those who truly deserve to die, using his own moral standards as the guideline. Hall received three Golden Globe (2007, 2008 and 2009) Best Actor nominations for for his performance on the Showtime series.

On January 9, 2009, Hall's representative announced that the actor eloped with his Dexter co-star, Jennifer Carpenter, on New Year's Eve 2008. The couple had been dating for over a year.Yahoo News: Dexter Brother and Sister are Husband and Wife (January 9, 2009)

• "...it's emotionless Dexter who gives the whole enterprise its air of detachment. What was a hitch last season is now a liability: He's such a cool operative, it's impossible to feel panicky for him - or even particularly uneasy. Despite Dexter's failed attempts at tension, the show's oddball cast of characters still has draw."—Entertainment WeeklyEW: Dexter Review (November 2, 2007)