Transport Scotland said Charles Ingram's camp had become a "safety hazard and distraction for drivers".
The 69-year-old was arrested for striking a messenger-at-arms with a mug as he was moved on from the site near Blair Atholl on Wednesday.
At Perth Sheriff Court, he admitted assaulting Roderick Stevenson at layby 52 on the A9, and was fined Â£1,000.
The road was closed in both directions briefly while Mr Ingram's camp was broken up, and he claimed he lashed out with the mug after feeling "overwhelmed".
Mr Ingram has lived at the side of the road near Blair Atholl since March 2012, with his camp expanding to include several tents.
Perth Sheriff Court was told concerns had been raised by passers by the local community, with fears for the safety of road users due to large home-made signs Mr Ingram would occasionally display.
Transport Scotland said the decision to evict Mr Ingram was not taken lightly, and said it was based on concern for his "personal welfare".
A spokesman said: "We have been working closely with Perth and Kinross Council, as the local authority responsible for care and welfare issues, along with Police Scotland, to ensure everything possible has been done to resolve this situation amicably.
"The extent of the encampment on the A9 has grown in recent months and it is now a safety hazard and distraction for drivers and we have no choice but to take this action.
"All partners remain on hand to provide any support we can to Mr Ingram to ensure that his welfare and possessions are protected."
A man who lived in a car at the side of the A9 in Perthshire for several years has been evicted.