"I'm here. With you all," the Nobel Peace Prize-winning Machado wrote on social media early Sunday.
Her return risks straining ties with the US Trump administration, which she has sought to cultivate as an ally since before it removed President Nicolas Maduro from power in January.
President Donald Trump has repeatedly expressed support for interim President Delcy Rodriguez, Maduro's former deputy, and hailed deals on oil production and other business ventures by US companies in the South American country.
Trump said in September it is too soon to consider democratic elections in Venezuela.
International energy firms committed last month to expanding projects in the country in a signing ceremony overseen by Rodriguez and US Energy Secretary Chris Wright.
Machado has said only a "serious, democratic government" can provide the stability needed by investors.
In June, she said she would do whatever it took to come home and help the survivors of devastating twin earthquakes that month, which killed at least 6500 people and left thousands missing.
Machado was barred by Maduro's government from exiting Venezuela but secretly left in late 2025 to receive the Nobel Peace Prize, after spending more than a year living mostly in hiding.
Her desire to return had caused friction in Washington, with US officials asking her to delay her trip, Reuters reported in June.
Machado did not disclose more details about her current location, or how she returned.
A faction of the opposition and the interim government held their latest session of talks this month, which aim to remake the top court and electoral council, among other goals, ahead of eventual elections.
They do not include Machado's political movement.
Edmundo Gonzalez, a former presidential candidate for Machado's movement who has been living in Spain, confirmed her return in his own post and said he would soon join her.
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