The man, who was in his 50s, died at the scene after being involved in a collision with a car and a lorry on the northbound exit slip road at junction 6 for Welwyn at 19:30 GMT on Tuesday.
No-one else was injured.
Hertfordshire Police said the rider appeared to lose control of his vehicle. Officers appealed for witnesses to come forward.
Updates on this story and more from Beds, Bucks and Herts here
A spokeswoman said the road was closed in both directions to allow investigations and repairs to take place but re-opened at about 08:30 GMT on Wednesday.
The A1(M) in Hertfordshire was closed for 12 hours overnight after an accident in which a motorcyclist died.