Llandaff Cathedral could be closed for up to three days while a new bishop is elected.
The college, made up of 47 people drawn from all over Wales, including all the Welsh bishops, will meet inside to nominate and vote on a confidential list of candidates.
The election follows the retirement of Dr Barry Morgan, who served as Bishop of Llandaff, as well as Archbishop of Wales.
The new bishop will be the 72nd Bishop of Llandaff, a diocese which serves nearly half the population of Wales as it includes most of Cardiff, the south Wales Valleys and the Vale of Glamorgan.
Once a bishop is elected, he or she will have up to 28 days to accept the position and will be formally confirmed in April