On 20 March 2015, Vatican yakazivisa kuti kunyange akaramba ari nhengo College of Cardinals, O'Brien aisazova kushandisa kodzero dzake kana mabasa somunhu Cardinal, kunyanya voting muna papal conclaves; akanga akaregerera pachake kubva kuitawo 2013 conclave
. O'Brien akafa mushure mekudonha musi wa 19 Kurume 2018, mazuva maviri mushure mekuzvarwa kwake makumi masere.