About 700,000 three and four-year-old children would be guaranteed 15 hours a week of preschool or kindergarten if Labor wins the next federal election.
Under the $1.75 billion plan, preschool would be extended to three-year-olds, giving children 600 hours of subsidised early childhood education a year.
Opposition Leader Bill Shorten will announce the policy in a speech in Melbourne on Thursday, making a pitch to parents ahead of the next election, due by May.
"All the research, science and experts make it clear the more early years learning we can give our kids before they go to school, it just absolutely quantum improves their learning experience at schools," Mr Shorten told the Nine Network.
Extending early childhood education to three-year-olds would bring Australia in line with the United Kingdom, New Zealand, France and China.
"Some of the smartest countries in the world are doing it. Australia has fallen behind," Mr Shorten said.
Labor will fund the plan by reining in tax concessions, including negative gearing and dividend imputation.
"We are able to do it because we're winding back some of the unaffordable tax concessions at the top end which we currently pay to some Australians," Mr Shorten said.
But Liberal frontbencher Zed Seselja said there was a significant hole in Labor's costings, with $1.75 billion unable to cover both three and four-year-olds.
"It appears even having reached into the pockets of many, many Australians, they still can't make their numbers add up," Senator Seselja told Sky News.
Megan O'Connell, director of Victoria University's Mitchell Institute, backed the two-year preschool plan as a way to lift national productivity.
"There is mounting evidence showing that two years of quality preschool helps children thrive in school and later in life," Ms O'Connell said.
She said extending education programs to three-year-olds was a minor cost compared with helping people who fail to secure employment later in life.
Mr Shorten said his party would work in partnership with the states and territories to deliver the plan, including setting enrolment and attendance targets, particularly for Indigenous and vulnerable children.