The goal of the new "savings and accountability" minister would be to find cuts of 0.5 per cent in spending — about $600 million a year on the province's $120-billion annual budget.
"I'm the sort of New Democrat who also believes we need to count the pennies," Horwath said at the legislature.
"There is a lot of waste in the system — I know that for sure."
Sounding at times more like a conservative, Horwath appeared determined to shake the legacy of former NDP premier Bob Rae, whose government from 1990 to 1995 was widely pegged as one that taxed and spent too much.
If citizens are expected to tighten their belts, she said, it's only right that government does the same.
Still, the NDP leader said, she would not go down the path proposed by Progressive Conservative Leader Tim Hudak, who has pledged to slash the public sector.
"I don't believe, like Mr. Hudak does, that kicking 100,000 people out of work is the right way to go," Horwath said.
The NDP, if elected on June 12, is promising to cut eight cabinet ministers and their staff to reduce waste and overlap.
It would also merge four of the five agencies running the province's electricity system and cap public-sector CEO salaries.
Horwath, who marked her 10th year as a provincial politician on Tuesday, said the NDP has been trying for years to get the minority Liberal government to tackle overlap and unnecessary spending to no avail.
"I actually believe that there's a lot of waste inside government right now," she said.
"After 10 years in office, it's clear the Liberals don't respect your tax dollars."
Having a cabinet minister dedicated to savings and accountability would "increase transparency, provide oversight and ensure that every department respects your tax dollars," Horwath said.
Hudak dismissed Horwath's plan as another typical New Democrat idea.
"Only the NDP could create a new bureaucracy to reduce bureaucracy," he said with a laugh.
Horwath, who triggered the election by refusing to support the Liberal budget, dodged a question about what she would do if voters again elect a minority Liberal government.
Following her announcement at the legislature, the NDP leader planned to head to St. Catharines and Brantford for mainstreeting and to meet local candidates.