And this week, he set a new benchmark by training his 200th winner this calendar year.
He had already overhauled Richard Hannon's record of 189 and his own best mark of 166.
A man of strident views and not shy about expressing them, Johnston has the words "Always Trying" emblazoned on his horseboxes which rack up starship mileages as they criss-cross the country from their North Yorkshire base in search of winners.
"Always Trying" is typical Johnston because it tells the public how he runs his horses and is also a telling shot at those trainers whose horses are not always doing their absolute best!
They say of Mark that he believes there are two ways of doing things - "his way and the wrong way".
And it is true he never shrinks from an argument, but that is simply because he is genuinely passionate about the sport.
He plays host to swarms of bees in his bonnet but expresses himself with a fierce intelligence and with no desire to take prisoners.
And he is one of those rare figures who has imprinted a style of running on his horses.
Johnston's horses often race bang up with the pace and find plenty when challenged.
So much so that they have earned a justified reputation for toughness and a willingness to battle that is matched by no other yard.
This season Johnston's haul has included winners at the top level.
They included Group One scorers Jukebox Jury and Awzaan, who won at Newmarket this month and looks set to hit the heights as sprinter next season.
Johnston said: "We hit the 100 mark at Royal Ascot and it's been an incredible season as the horses have stayed healthy.
"I've had slightly fewer horses this year with 200 at the absolute peak and the percentage strike- rate is higher than last year."
One of the most striking things about Johnston is that his hunger for the game is as strong as ever.
His horses are fit and graft hard and he has stripped away much of the smoke and mirrors approach favoured by trainers who like to baffle rather than inform.
I asked one of my London-based racing friends, who is a great Johnston admirer, what he liked most about the trainer.
He recited a long list of qualities - then added: "And the most important thing is that he lives a really long way away from where I do so I don't have to argue with him every day!"
Read Alastair Down every week in the Racing Post
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