Environment minister Mahinda Amaraweera told parliament legislation was being drafted to stop imports of plastic goods, including polythene, that end up in landfills. Officials said it would be introduced within months.
"Plastics are doing untold damage to our wildlife -- elephants, deer and other animals," Amaraweera told AFP shortly after his announcement.
"We need to take immediate action to arrest this situation."
Sri Lanka has already banned the manufacture or import of non-biodegradable plastic used for wrapping food and shopping bags since 2017.
Endangered wild elephants are protected in Sri Lanka by law although clashes with farmers are claiming a heavy toll on both sides.
President Gotabaya Rajapaksa has given wildlife officials two years to implement a plan to reduce human-elephant conflict that has claimed the lives of 607 elephants and 184 people since last year.