The 22-year-old, who was 21 at the time of winning, is the youngest ever chef to take the title in the ten series of the BBC show.
Finalists were challenged to create the best three-course meal of their lives for judges Marcus Wareing, Monica Galetti and Gregg Wallace.
“To be the last man standing is unbelievable,” said Johnston. “I feel like I’m dreaming – it’s a dream come true. I’ve loved absolutely every minute of it. My parents will be very proud.”
Craig’s winning menu began with torched mackerel and mackerel tartare, with salt-baked beetroot, horseradish milk gel, beetroot pickled onions, garnished with beet leaves and a dorrell and dill iced granita.
His main course was roasted squab pigeon with thyme-infused pomme anna, a ras el hanout-spiced pigeon leg pastilla, charred and roasted thyme onions with a nasturtium oil, radicchio leaves and a red pepper and tomato ketchup, finished with pigeon sauce.
Craig’s final dessert was sauterne and yoghurt mousse, basil marshmallow, bergamot curd and olive oil crumble, topped with frozen lemon cells and verbena frozen rocks.
Wareing was rendered ‘speechless’ during the tasting of the winning menu.
Galetti told Johnston: “This speaks volumes about where you started and where you are now as a chef. You’ve always given us delicious, beautiful food, but it’s on another level now. Where are you going to be, five or ten years from now?”
Johnston trained at two-AA Rosette Maidenhead restaurant Boulters under Chef Daniel Woodhouse, and whilst working there achieved NVQ Levels 2 and 3 in Professional Cookery from Henley College.
“As the next step in my career, I'd love to focus more on fine dining and push myself to learn more whilst I can,” he said.
“My ambitions longer term are to learn as much as I can still while I'm young, and hopefully when the time is right in years to come step up to my own head chef role.
“My career is just beginning. I’ll have to hold on tight as it’ll be a bumpy ride, but I’m looking forward to it!”
The other top four finalists were Louisa Ellis (aged 22), Steven Lickley (aged 25 at time of filming) and Jamie Park (aged 27).