Supposedly final talks in South Korea in 2024 towards an agreement failed, and a renewed effort in Geneva last August likewise collapsed in overtime.
Delegates from dozens of countries held three days of "informal" discussions in Japan ending Tuesday, which were not expected to result in any official announcement.
However, a source involved in the talks said they had gone better than feared.
"Given the context of the more or less collapse of the negotiations in August, I think this is a restart of the conversation," the source said.
The talks were "constructive" and "could provide... a pathway towards agreement", they added. "It could have been a lot worse."
The negotiators will meet in Dakar for another meeting in May, the source said.
Japan's lead negotiator Satoshi Yoshida also told AFP the negotiators "had good discussions" and more meetings would be held in the coming months.
More than 400 million tonnes of plastic are produced globally each year, with half for single-use items.
A large bloc of states wants bold action such as curbing plastic production, while a smaller clutch of oil-producing states wants to focus more narrowly on waste management.
Countries that were present in Tokyo include big oil producers like Saudi Arabia, Russia and the United States as well as island states Antigua and Barbuda and Palau, plus China, India and the European Union.
The UN's environment chief told AFP in an interview in October that a global treaty remains "totally doable".
"No-one has walked away and said, 'this is just too hopeless, we're giving up,'" United Nations Environment Programme executive director Inger Andersen said.
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