The M1 was closed northbound between J12 for Flitwick and J13 for Milton Keynes South following a 'serious collision' earlier.
Traffic was queueing on all approaches to the closure and motorists were being advised to avoid the area.
A closure had been in force since around 1.30pm this afternoon with Bedfordshire Police and other emergency services at the scene.
The southbound carriageway re-opened after 7pm with the northbound side re-opening just before midnight.
Highways England Traffic Officers were also attending to assist with traffic management.
Road users travelling northbound were advised to follow the hollow black diamond diversion symbol and road users travelling southbound were advised to follow the hollow black square diversion symbol.
