Mark Bonnar (Chris) was only supposed to be in the show's pilot episode. He did such a great job with the role that he was written into the series.
Rob Delaney came to prominence as a comedian via humorous posts on Twitter, gaining over a million followers by 2016. He met "Catastrophe" co-creator Sharon Horgan via the social networking service, where their shared senses of humor inspired them to write together.
All season 4 episodes were directed by Jim O'Hanlon, replacing Ben Taylor, who directed every episode of seasons 1-3. Jim has also directed episodes of "The Bill," "Waking the Dead," "Shameless," "Mutual Friends," "A Touch of Cloth," "Sleepy Hollow," "Marcella," and "The Punisher."
The role of Sharon and Rob's son, Frankie, is shared between twin brothers Dexter and Sonny Hyman, who won the role after auditioning at a casting call for season 2.
"Catastrophe" creators Sharon Horgan and Rob Delaney insisted that the show should have a high joke-to-page ratio as a way to buck the trend of shows that were more hybrids of drama and comedy.