Election rules prevented the leaders from running the ads over the past two weeks, but that blackout period ended at midnight.
The Liberals are rolling out a TV commercial across the province, as well as 35 different radio spots, each voiced by Premier Kathleen Wynne.
The ad shows Wynne talking about her platform, but also slamming Tory Leader Tim Hudak's plans to cut 100,000 public-sector jobs.
Liberal party officials say the commercial isn't a negative ad, but one that contrasts the choice voters face in the June 12 election.
The Tories are also putting out a radio ad targeting the Liberals and their costly decision to cancel two gas plants ahead of the last election at a cost of up to $1.1 billion.
The NDP made an unusual move Wednesday, taking out a full-page ad that wraps around the front of the conservative Toronto Sun newspaper. The ad, designed to resemble a Sun front page, has an image of both Wynne and Hudak with a headline that says "nonsense."
The back page of the ad touts Leader Andrea Horwath's plan to cut small business taxes, lower rates for auto insurance and cut public-sector CEO salaries.
Party strategists told the Canadian Press that the NDP are trying to target undecided voters with the ad, particularly those who have voted Conservative in the past but don't like Hudak or his policies.