Cr O'Malley a first-term councillor and key figure behind the "Own the Factory'' chocolate campaign confirmed his intentions this afternoon.
His announcement came just days after three-term mayor Dave Cull confirmed he would not seek a fourth term as mayor in October.
Cr O'Malley will join Cr Aaron Hawkins as the only incumbent DCC councillors to have confirmed bids for the mayoralty.
Crs Lee Vandervis, Christine Garey and Andrew Whiley all potential challengers are still keeping their cards close to their chests, as is Dunedin businessman Barry Timmings.
Scout Barbour-Evans and Carmen Houlahan both candidates from outside the council have also confirmed their plans to run for the mayoralty.
Nominations for local body elections open on July 19.