Mark Wahlberg was originally attached to play Perry Smith, but dropped out in August 2004. He was replaced in October 2004 by Mark Ruffalo, until he dropped out as well.
This film appeared not long after the film Capote (2005). While Infamous goes deeper into the background of the killers, Capote focuses intensely on the relationship between Capote and Smith. As such, the two films could be considered to be companion pieces.
Sigourney Weaver talked to Babe Paley's daughter while researching for the role. The girl told her about her mother's habit of covering her teeth whenever she smiled, which Weaver actually did in the movie.
Douglas McGrath heard a story about the real Diane Vreeland making her maid iron the money. He liked that so much that he included it in the movie.
This film and Capote (2005) were written and produced almost simultaneously but Bennett Miller's film got released first and received several accolades during the awards season.