"We need the faces around the table that represent this diverse city. I want to encourage people to stand up and put their names forward."
Ms O'Leary said she will also stand for councillor for one more time, but will be putting all her effort into the mayoralty race.
In a statement announcing that she would stand for mayor, Ms O'Leary has targeted Mayor King's platform of truth and transparency.
"Leadership by surprise isn't working. It's deeply disappointing that his actions have totally failed to deliver on this promise. Under current leadership, residents find themselves enduring soaring rates and see their city plunging further into a debt".
Earlier in the day Hamilton News spoke with Hamilton mayor Andrew King who confirmed he will stand again for the mayoralty and said he has led with transparency, and believes he has more to give as Hamilton's mayor.
"Very few things are in the public excluded parts of the meeting," Mayor King said.
"I've continued to make myself available to anyone who wants to make an appointment and I use my Facebook page to continue to share what is happening with council and around the city.
He said being mayor was all about listening to the people of Hamilton.
"For 30 years people have talked about opening up the Peacockes growth cell, for 20 years we have been talking about a new library for Rototuna, and for as long as I remember we have talked about opening up the city to the river, and under this council we have done it."
Candidate nominations for the 2019 local body elections open on July 19, and polls close on October 12. The new council will be inaugrated on October 24.