The Second Severn Crossing was closed in both directions on Monday night after a man climbed up one of the main supporting cables.
The £300m crossing opened in 1996, 5km from the original bridge
Gwent Police said they shut the bridge after he threatened to jump into the estuary at about 2130 GMT.
Police said after about an hour-and-a-half the man, from Burnham-on-Sea in Somerset, agreed to surrender himself.
A man was arrested and was being questioned at Newport central police station.
A police negotiator was called to the scene, along with other emergency services.
South Wales Fire Service were on standby and the Severn area rescue lifeboat took two teams of coastguards to the scene.
Drivers were diverted via the M48 and the first Severn Bridge while negotiations took place.
The crossing reopened just after 2300 GMT.