Green MPs will "hold Theresa May's feet to the fire" if the Tories win the election, Caroline Lucas will say as her party sets out its key priorities.
The Greens are due to announce their plans for a "confident and caring country" in central London on Monday morning.
They will promise to "reverse the privatisation of the health service" by introducing an NHS Reinstatement Bill and give people a referendum on the terms of a Brexit deal.
The party will also pledge to protect freedom of movement and immediately guarantee the rights of EU citizens.
Other plans set to be announced at the Green Guarantee launch include protecting the environment and bringing forward proposals for a basic income and shorter working week.
Ms Lucas, the party's co-leader, will say: "The Green Party has big, bold ideas to create a confident and caring country we can all be proud of.
"That means protecting our environment for our children and grandchildren. Saving our NHS from crisis and ridding it of private sector profiteering.
"It means giving people a proper say on the Brexit deal, not shutting them out of the process. And it means exploring changes to our economy to make it fairer and fit for the future.
"Green MPs elected on June 8 can be trusted to protect our public services, fight for a close relationship with the EU and truly hold whoever is in Government to account.
"If we do end up with a Tory Government you can be sure that Green MPs will hold Theresa May's feet to the fire."