The 58-year-old was banned for showing "a reckless disregard" for rules on horse welfare.
The ban relates to the running of late horse Striking Article eight times after he had undergone a denerving operation called a palmar neurectomy, and the administration of anabolic steroids to other horses.
""I am not the best man at reading the rules of racing," Johnson told BBC Sport.
"I admitted that the vet de-nerved the horse but I didn't know it was called a neurectomy. The horse was in pain with the state of his feet, and the corns.
"We relieved the pain of that horse to run eight times, and the horse won three races."
The County Durham-based trainer had held a training licence since 1984 and enjoyed many notable successes during his career, not least with triple-World Hurdle winner Inglis Drever.