Horwath was in her home riding of Hamilton Centre on Saturday morning to cast her ballot in the first day of advance polling for the June 12 provincial election.
Her appearance in Hamilton comes amid speculation that she is at least mulling a possible working arrangement with Tim Hudak and the Tories in a minority parliament.
Horwath has left the door open to working with other parties after the election.
The Liberals, first under the leadership of then Premier Dalton McGuinty and then under his successor, Kathleen Wynne, survived more than two and a half years of minority government at Queen's Park with the support of the NDP.
“I want to be clear: I am running to be premier of this province,” said Horwath, responding to a reporter’s question about whether she would work with a possible PC minority.
“What I can tell you is I will never support any plan that fires 100,000 hard-working people in this province,” she said, citing Hudak's plan to cut tens of thousands of public-sector jobs in a bid to balance the provincial budget by 2016-2017.
However, she did not rule out working with the Tories in a minority legislature at Queen’s Park.