Finance Secretary John Swinney said he hoped the funding - which comes on top of £255,000 from the UK Government - would mean hazardous waste could be removed "in a timely fashion".
After an inspection by the Scottish Environment Protection Agency in 2012, 13 households in the Blanefield area of east Stirlingshire were told their land was contaminated with traces of lead and arsenic.
The chemicals are said to be a remnant from a Victorian printworks which has long gone out of business.
That leaves the current owners of the land liable for the clean-up costs, which amount to more than £600,000 in total.
The funding from the Scottish Government, together with cash from the UK Government and Stirling Council, means the work should now be able to proceed.
Blanefield resident Martin McGougan said after a "very stressful" two years for the residents involved, "a weight has been lifted off our shoulders".
He added: "We've had huge bills that we've had no ability to pay hanging over our heads and it's been a terrible financial and emotional burden for us.
"The Scottish Government's fantastic contribution means that for the first time in two years we can take our lives off pause and get on with normal life again.
"We are absolutely delighted with the Scottish Government's contribution of up to £300,000. It's a huge amount of money to us and means all the work can now be done."
Mr Swinney said: "It is inexcusable that residents affected by the contaminated land have not only had to worry about the risks to their health, but they have had to live in fear of being held financially responsible for the cost of the removal of the waste.
"That's why we have now pledged up to £300,000 to help residents meet the costs of cleaning up this contaminated land."
He added: "Landfill tax and the decision to exempt disposals of contamination is currently a matter for Westminster.
"If the UK Government waived the tax costs associated with the clean-up when the lead and arsenic was first discovered, residents would not have had such an ordeal.
"The Scottish Government is already taking steps to ensure that once landfill tax is transferred to Scotland other residents cannot find themselves in this situation.
"I now hope our contribution means the hazardous waste can be removed in a timely fashion, and people in Blanefield can get on with their lives."