The leader of the third party says New Democrats are a realistic alternative to what she calls the "corrupt" Liberals.
The Progressive Conservatives, she says, would set Ontario back with deep public-sector cuts.
Both Premier Kathleen Wynne and Tory leader Tim Hudak have tried to frame the election as a two way race, while largely dismissing the NDP.
But Horwath is shrugging off suggestions that Ontarians might choose to ignore the New Democrats to try to stop the Liberals or PCs from winning office.
Instead, she says New Democrats would not waste taxpayer dollars as the Liberals have done with decisions like cancelling two gas plants at a cost of up to $1.1 billion.
"This is an important election," Horwath said in Hamilton on Saturday after voting at an advance poll.
"We do not have to have a Liberal government that is corrupt, that wastes our tax dollars, that doesn't respect the hard-earned money that you send to Queen's Park, and we don't have to have a Hudak government frankly that makes no sense whatsoever."
Horwath says the NDP would not slash 100,000 public sector jobs — a direct jab at Hudak's plan to cut 10 per cent of the public sector.