Rahm joins Jake for Nightcrawler
Jake, who is also co-producing the movie, is to star as a "driven" young man who soon discovers the nocturnal world of freelance crime journalism in Los Angeles.
Bill Paxton will also appear in Nightcrawler, which will mark the directorial debut of The Bourne Legacy's screenwriter Dan Gilroy.
Kevin played one half of Wisteria Lane's gay couple Lee McDermott, alongside Tuc Watkins as Bob Hunter, on Desperate Housewives.
He will return to Mad Men for its seventh and final season, which will be aired in two parts over 2014 and 2015.