From 2015-2019, she co-starred and co-wrote the sitcom "Catastrophe" with American comic Rob Delaney. The two first met on Twitter, and because they made each other laugh decided to work together. They have both said "Catastrophe" was broadly based on their own personal experiences. In it she played Sharon, an Irishwoman living in London who becomes pregnant by Rob, an American she meets while he is on a business trip to London. Carrie Fisher played his mother. It was an instant critical success and after the second episode of the six-part series was aired Channel 4 announced it had commissioned a second series. Horgan was nominated for a Best Female Comedy Performance BAFTA for her role. in 2016, Channel 4, ordered a third and fourth season.