The former British and Irish Lions and England captain has been banned from driving for 49 days after being caught speeding at over 100mph on the M5 earlier this year.
Johnson was stopped on the M5 at Puriton in Somerset this August after police clocked his Range Rover "overtaking all other traffic" in the fast lane between Junctions 24 and 23 near Bridgwater, Somerset.
The big 4x4 that also carried his wife and children was clocked at speeds of up to 107mph before police decided to step in. Johnson admitted speeding at Taunton Magistrates' Court and was fined £800, ordered to pay an £80 victim surcharge and £35 costs as well as being handed the ban.
According to his defence, Johnson "admitted his guilt at the first available opportunity and co-operated with police."
Stephen Gooden, defending, added: ""When he was stopped, the traffic was light and he was in a very powerful vehicle.
"He wasn't going to risk his wife, daughter and son's safety. He understands the seriousness of the matter."
Johnson's defence told the court that he relies heavily on his vehicle now that he is self-employed.
After the hearing, Johnson - who won 84 England caps and lifted the World Cup in 2003- headed off to a charity dinner in London by train.