Firefighters used a ladder to approach the man, who spent around an hour on a narrow ledge on the outside of the ancient amphitheatre before being persuaded to climb safely inside.
His motives were unclear, but reports said it appeared to be some kind of protest rather than a suicide attempt.
Videos showed the man pacing and shouting while a crowd of onlookers gathered below.
According to some reports, the man is a tour guide who recently lost his licence. But others said he was calling for the right to operate food and drink trucks near Rome's historic monuments, after the city council threatened to crack down.
Firefighters had laid out inflatable mattresses to break the man's fall in case they were unable to persuade him to descend.
The Colosseum, which with 4 million visitors a year is one of Italy's biggest tourist sites, remained open on Tuesday afternoon.