McDonald's has promised to eliminate foam packaging from its global operations by the end of 2018.
The move follows pressure from activist shareholder group As You Sow, which in 2017 gained the support of around a third of shareholders in a vote calling for McDonald's to assess the impact of its use of polystyrene in cups and trays.
In December As You Sow re-filed the motion for another vote in 2018. It has claimed victory after the burger chain quietly updated its packaging policy.
"Through our work with @mcdonalds, they have pledged to be #foamfree by the end of this year! Tis the first fast-food giant to commit!" the group tweeted.
McDonald's said on its website: "We... plan to eliminate foam packaging from our global system by the end of 2018.
"While about 2% of our packaging, by weight, is currently foam, we believe this small step is an important one on our journey.
"Most of the fry boxes, sandwich clamshells, wrappers, cups and other items that help to keep McDonald's food ready to eat are made of fibre that is paper or cardboard."
The firm said 64% of fibre-based packaging came from certified or sustainable sources and it aimed to increase this figure to 100% by 2020.
In December As You Sow said: "McDonald’s phased out its use for hot beverage cups in the US in 2013, but still uses it in overseas markets where plastic pollution migration into waterways is highest.
"Rarely recycled, polystyrene is found on ocean beach cleanups frequently. The material breaks down into indigestible pellets, which marine wildlife often mistake for food, resulting in the deaths of fish, birds, turtles, and whales.
"Its hazardous constituent chemicals have been shown to accumulate water borne toxins in a short time frame, and the International Agency for Research on Cancer has determined that styrene, used in the production of polystyrene, is a possible human carcinogen."