Despite being an outsider in the betting stakes, the 38-year-old Norwegian was appointed Neil Lennon's successor on a 12-month rolling contract.
But should anyone really be surprised?
The "Norwegian Jurgen Klopp," as he has been christened, embodies Celtic's overall strategic objectives.
He is young, has the potential to grow even more as a manager and already has experience operating in a somewhat restrictive transfer environment, relying on effective scouting rather than excessive spending.
Over the course of his six-year spell as manager of small Norwegian side Stromsgodset, Deila transformed the club from a bottom-half team striving to stay in the top division to cup winners in 2010 and league winners three years later.
The progress he made is easily traceable. After finishing 11th and 12th—in a league of 16—in his first two campaigns, the young boss led his side to seventh and eighth in the next two. By the final two years of his tenure, Stromsgodset finished second in 2012 and, finally, as champions last season.
On the pitch, Deila has a distinct philosophy: fast, attacking football.
Favouring a 4-3-3 system with offensive full-backs—ideal for current Celtic defenders Emilio Izaguirre, Adam Matthews and Mikael Lustig—Deila places considerable emphasis on youth and development to carry out his vision successfully, as he told a press conference upon his confirmation as manager (per BBC Sport):
It's about winning trophies, getting into Europe, developing players and creating a culture inside the club. The culture of developing is everything. I have to think about the process and what to do on the pitch. Then results will come.
Without development, you won't get results. The board will see what I'm doing with the club. If I do well and make people happy, push the right buttons, we'll get results.
Indeed, the average age of his 2013 Stromsgodset squad—which brought home only the second championship in the club's history—was under 23.
Deila used 26 players that campaign—only four of whom were older than 30. Encouragingly for the likes of the returning Tony Watt, he also used no fewer than 13 players aged 21 or under, including six teenagers.
One of those young league winners was current Celtic midfielder Stefan Johansen, whom Deila transformed from a winger to the central midfield playmaker Lennon purchased in January. The 23-year-old made public the admiration he has for his former boss as he was confirmed in his new role:
A lot of question about Ronny Deila have been asked here. Great person and a great manager and im looking forward to work with him again.— Stefan Johansen (@stefanjohansen) June 7, 2014
Of course, the deeply cynical will ask questions based on the practicality of trying to implement that particular philosophy in a Scottish football environment.
They may even point to Tony Mowbray—the last footballing idealist to take over at Parkhead—as evidence of someone who endeavoured to place philosophy ahead of practicality and failed.
And, unlike Norway's Tippeligaen, where around half the teams play on artificial turf conducive to passing football, the SPFL is not noted for the standard of its pitches. This could make some away fixtures inherently tricky for a manager intent on showcasing an attacking, possession-orientated brand of football.
However, Deila told the press conference on his first day as Celtic manager that home matches are the time to entertain the fans, suggesting he is willing to adopt a slightly more cynical method—such as counter-attacking—when the situation calls for it.
This could prove ideal for the club in European competition, where matches against bigger sides with far more technically-adept players have necessitated an ultra-defensive approach in the past.
Indeed, Deila's decision to bring 6'6" target man Peter Kovacs back to Stromsgodset at the age of 33 in 2012 surely points to an intellect in identifying the shortcomings of his own overarching philosophy.
Kovacs provided a different option to what Deila otherwise had at his disposal and paid his manager back nicely—netting 22 times in his first season working under him.
The big Hungarian has proved the exception rather than the rule for Deila's transfer dealings.
While transfer business remains somewhat of an unknown quantity due to the stark difference in size between Celtic and Stromsgodset, there is plenty of evidence that hints Deila will keep with Celtic's recent policies.
He seems to prefer spending only when he loses key players, for instance. And, even then, he tends to buy replacements younger than those who have left.
In season 2009, for instance, he shipped out eight players with an average age of just over 28. In return, he brought in eight with an average age of 23.
Will Ronny Deila be a success at Celtic?
This trend continued until his move to Glasgow last week. In each of the past five seasons, Deila has acquired no more than he has lost and always the average age of his new recruits has been lower than those who left.
While candidates such as Henrik Larsson, Owen Coyle and Malky Mackay may have been altogether safer choices where the fans are concerned, the appointment of Deila represents no real surprises in terms of the club's recent signing philosophy.
Given he has the unique gift of time in his favour—with no real challengers domestically—the comparisons with Mowbray may just be rendered obsolete.
Of course, as he takes his first job in a foreign country, the Celtic fans and board alike will have to allow him time to both adapt to his new surroundings and implement his philosophy.
If they—and, perhaps more importantly, the players—buy into his methods, then Scottish football as a whole may benefit from the example.
All statistics referenced in this article are taken from TransferMarkt.co.uk