The boat, La Vagabonde, carried the Swedish campaigner, who refuses to travel by plane, across the ocean so she could attend the COP25 climate summit in Madrid. She will spend the day holding meetings with Portuguese climate activists and resting before her departure for Madrid.
More than 150 supporters turned out to greet Thunberg as she came ashore. Among them was the leader of Portugal's People Animals Nature party, Andre Silva, who praised Thunberg for her role in "tackling the greatest crisis of our times."
"She is prioritizing an increasingly urgent issue in a way politicians just aren't," he told Reuters.
Her arrival in Lisbon coincides with the release of a bleak report by the Geneva-based World Meteorological Organization, which warns that the past decade is almost certain to be the hottest yet recorded.