Alan Johnston, 45, was handed over to Palestinian officials after what was reported to be a late-night deal with the al-Qaeda-inspired group holding him.
The release comes a day after the Islamist Hamas movement, which recently seized control of the Gaza Strip, drastically increased its pressure on the so-called Army of Islam group said to be holding Johnston, surrounding its presumed hideout and arresting its spokesman.
Johnston's release brings to an end a 16-week ordeal during which the journalist was repeatedly threatened with death, appearing at one point in a videotaped message wearing an explosive suicide belt which his captors said they would detonate should any attempt be made to free him.
The kidnapping played out against the backdrop of an ongoing power struggle in the Palestinian territories between the Hamas and Fatah movements, which has resulted in scores of deaths and retaliatory kidnappings.
Commenting on Johnston's release, the exiled Hamas leader Khaled Meschaal said it demonstrated that his movement, which orchestrated it, was now in complete control of events in Gaza.
Johnston, who was the last Western reporter still working in Gaza since the outbreak of fighting there, was held longer than any other hostage seized in the Palestinian territories.
He was greeted by BBC colleagues and well-wishers after arriving at the home of a local Hamas leader, who draped him in a Palestinian flag and welcomed him back.
