The 23-year-old Leicester lock spent two seasons playing club and provincial rugby in New Zealand, and three years ago was lining up alongside the likes of Va'aiga Tuigamala, John Timu, Stu Forster, Craig Dowd and Blair Larsen in the Blacks' Under-21 side.
However, he came home, and in the past 10 months has achieved more in the game than most players do in a career. An England debut in January was followed by a Cup winners' medal for the Tigers in May - not to mention the decisive try - and an injury to Wade Dooley led to two Test matches for the Lions this summer.
On Monday, along with other participants on that Lions tour, Johnson was sipping tea with the Queen and the Princess of Wales at Buckingham Palace, and reflected: 'I suppose you could say that things have happened in a bit of a rush.' He has clearly learned his extrovert rhetoric from his club captain, Dean Richards.
Johnson, in fact, is as placid a character as you would expect a bank clerk to be, although for 80 minutes on a Saturday afternoon, it is the rough equivalent of Clark Kent nipping into a telephone kiosk to slip into his tights. Johnson exchanges his suit for a jersey several sizes up from extra large, and hurls his 6ft 7in, 17st 10lb frame into a form of combat that is a bit like dodgems without cars.
The line-out, which is where Johnson's contribution will be crucial tomorrow, is where he first made his mark at Leicester - in something of a literal sense - as a 17-year-old youth player. Picked for a third team game, he was given the traditional young upstart's initiation test by a gnarled veteran from Moseley, whereupon Johnson returned the punch with a right hander of his own, and inquired as to whether they could now get down to the business of playing rugby.
His first big game for the Tigers was in the 1990-91 season, when Leicester had gone down 9-3 at home to Bath in the league, and were due to face the same opponents away, in a Cup match, the following Saturday. Johnson was picked only because of injuries to both Leicester locks, and had an outstanding game in an unexpected 12-0 victory.
He had, however, already had a serious grounding in senior rugby in New Zealand, having gone there for an extended holiday after leaving school. He made such an impression that he was given a job by the New Zealand National Bank to allow him to extend his stay for another season, and would have returned for a third winter Down Under but for an operation on a dislocated shoulder.
His England debut came in January when he was due to play for the B side in Leicester, but was called down to Twickenham at 24 hours notice because of an injury to Dooley, and he eventually played in England's 16-15 victory.
'Like everyone else,' he said 'it was the pace of the game - mentally as well as physically - that made international rugby so different. When you play your first game, you are really looking just to survive it, but now that I have played twice for the Lions, it becomes more a case of wanting to become more involved - to have an influence on the game.'
Given his experience both of New Zealand rugby and of his two Lions' Tests against them, Johnson should be pretty well equipped to know just what it will require for England to beat them this afternoon. 'The short answer,' he says, 'is a heck of lot. But having said that, I fancy us to do well.
'New Zealand rugby is terrifically high profile - when I played Under-21's there we were live on TV - and is much more physical and intense. This match to them will be pretty well life or death, just as it was when they came out for the decisive Test having just seen us draw level at 1-1.
'The whole tour was on that last game, and they played very well. However, whether that series finished 2-1, 3-0, or 0-3 wouldn't make any difference to this one. It is still England versus New Zealand with everything to play for, and it will be a bloody hard game.
'Whenever you take the field against any New Zealand side you know you have got to be on top of your game to beat them, but having played three times now at international level, I think there is a very fine line between achieving and not achieving.
'They will try to impose their game upon us, and we must try to do the same to them. It is a mental and physical battle of wills, and if mistakes can sometimes be glossed over in club games, errors, missed tackles, and failing to take your chances are invariably fatal in internationals. At this level you have to be ruthless - and I mean that in the rugby sense.'
Johnson's quiet demeanour does not suggest a ruthless streak, but the furniture at his parents home in Market Harborough has not always survived his mock scrummaging battles on the carpet with younger brother Will, who plays at No 8 for Leicestershire's Under-21 side.
Johnson wouldn't say who generally comes out on top, but smiled: 'it can get pretty competitive.' There is, in fact, a strong competitive streak running through the family, and his 49-year-old mother Hilary, a PE teacher, is a regular marathon runner, including London, Paris and New York.
As with all modern top-class rugby players, the days when training began in the pub and ended in the curry house have long gone, and Johnson has his own personal programme designed by expert advisors to the England team. 'Everyone has different disciplines' he said, 'but I do a lot of work on the rowing machine, which helps with endurance, and obviously do a lot of weights, which is for body strength.'
All of this has to be squeezed in around his job with Midland Bank, but top-flight rugby nowadays makes so many demands that, in terms of time, Johnson has to make more withdrawals than deposits. 'There are only supposed to be four weeks holiday, but what with trips to Canada, New Zealand and Lanzarote, I've had around 11 already this year.'
Mind you, the bank also gets its mileage out of celebrity status, and neither should the time off necessarily be regarded as holiday. Some of these games are so tough on the facial features that the bank would probably give Johnson the next few days off on the grounds that to have him peering out from behind the grill would only frighten the customers.