A Dáil by-election was held in the constituency of Carlow–Kilkenny in Ireland on Friday, 22 May 2015, to fill a vacancy in the 31st Dáil. It followed the resignation of Fine Gael Teachta Dála (TD) Phil Hogan on his appointment as European Commissioner. It was held on the same day as national referendums on marriage equality and the age of eligibility for election to the office of president.