The firm, which owns brands including Dove soap, Ben and Jerry's ice cream and Marmite, would cut annual use from the current 700,000 tonnes of a year to no more than 350,000 tonnes.
The move comes as multinational firms face growing pressure to cut the use of plastics which are polluting both land and sea.
"Plastic has its place, but that place is not in the environment. We can only eliminate plastic waste by acting fast and taking radical action at all points in the plastic cycle," Unilever chief executive Alan Jope said in a statement.
Plastic has its place, but that place is not in the environment. Today, we’ve committed to halving our use of virgin plastic, and to collect and process more plastic packaging than we sell, by 2025. #Plastic #PlasticWaste https://t.co/kIJxw5L06p pic.twitter.com/GtnJdRsgOU
— Alan Jope (@alanjope) October 7, 2019
But Jope told the BBC that the company -- whose 400 brands also include Knorr, Lipton tea and Magnum ice creams -- was also trying to remain "relevant".
"We do believe in trying to remain relevant for younger groups of consumers, and we know that millennials and Gen-Zennials, the next wave, really care about purpose and sustainability, and the conduct of the companies and the brands that they're buying," he told the broadcaster.
Of the 350,000 tonnes of "virgin plastic" Unilever will cut, it said 100,000 tonnes will come from an outright reduction in the use of plastic packaging, for example by making reusable or refillable packs, using alternative packaging or "naked products" that use none at all.
The other 250,000 tonnes of the reduction will come from using recycled plastics.
The firm said it would also "help collect and process more plastic packaging than it sells".
Unilever said it was the "first major global consumer goods company to commit to an absolute plastics reduction".
Alternative methods it has tried recently include shampoo bars, refillable toothpaste tablets, cardboard deodorant sticks and bamboo toothbrushes.
The world produces more than 300 million tonnes of plastics annually, the UN says, with much of it ending up in the oceans.
Companies are coming under increasing pressure to act.
In September, 19 companies including Unilever, Nestle, Google and L'Oreal announced a "coalition" to protect biodiversity at the UN climate summit in New York.
Swiss group Nestle has made a similar pledge to the one by Unilever, saying that it will make all of its packaging reusable or recyclable, and raising to 35 per cent the proportion of its plastic bottles that is made of recycled material.
US coffee giant Starbucks is meanwhile planning to ban plastic straws by 2020 while Walt Disney Co said it would replace small plastic shampoo bottles at its resorts and many British supermarkets have drastically cut down plastic bag use.
There was also a pledge at this summer's G20 in Osaka to tackle marine plastics pollution, although environmentalists attacked it for being vague on detail.
"There is a general awakening of conscience among consumers which is alerting both governments and producers," Gregory Bressolles, professor of marketing at Kedge Business School in France, said.
However he warned against "attempts at greenwashing" by businesses. "Greenwashing" is a term used to critics to describe efforts by companies to promote often spurious environmental measures for commercial gain.
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