Born in Nürtingen, Germany, Jaissle came through Stuttgart's academy, where he was coached by a young Thomas Tuchel, with whom he has remained close friends.
His playing career at Hoffenheim was cut short by an ACL injury that forced his retirement at 25, but it was there that Ralf Rangnick first identified his coaching potential, pulling him into RB Leipzig's youth setup. From there, Jaissle followed Alexander Zorniger to Brøndby as assistant manager before Rangnick brought him back into the Red Bull fold at Salzburg, first with the under-18s, then at Liefering, before he was handed the Salzburg first team at just 33.
He delivered immediately, winning back-to-back Austrian Bundesliga titles and an Austrian Cup, and taking Salzburg into the Champions League knockout stage for the first time in the club's history. Jaissle has described his coaching identity as shaped directly by that background.
"Due to my past at both Salzburg and Leipzig, I have this identity in my blood to put stress on the opponent as high up the pitch as possible. I want my teams to play in a really intense and aggressive way," he told GiveMeSport.
On tactical flexibility, he has said: "It's not about copying, exactly, but seeing interesting things, creating your thoughts about it, and then, if it fits, you can bring it into your way of playing."
Salzburg sacked him in 2023 after he pushed to leave for Al-Ahli, with the club's managing director Stephen Rider saying at the time: "We believe that a coach who is so intensely concerned with a possible change of club just two days before the start of an important season should not be there for this opener either."
The abrupt nature of the exit reportedly rankled inside the club; Salzburg's sporting director at the time, Christoph Freund, later gave a diplomatic verdict on his former coach's pull, telling 90minuten.at: "Jaissle is certainly a coach who is much sought-after on the international market."
Others were less generous about how he left. A Goal.de retrospective on the upheaval noted that, unlike predecessors Marco Rose and Jesse Marsch, Jaissle had always come across as "noticeably more distant, more unapproachable," and that his sudden departure "caused outrage" among a fanbase who felt blindsided.
That reserved reputation stretches back to his playing days. Andreas Ibertsberger, a former Hoffenheim team-mate, once recalled that Jaissle "wasn't the typical footballer," someone who kept a low profile off the pitch and had little interest in the trappings that came with it — a trait that appears to have followed him into the dugout.
Since moving to Jeddah, Jaissle has won back-to-back AFC Champions League titles and a Saudi Super Cup, prompting rival coach Sabri Lamouchi to call his Al-Ahli side simply "excellent" after a defeat earlier this year. He has also earned comparisons with Julian Nagelsmann for his progressive approach.
Not everyone is convinced he is the right fit for Newcastle. ESPN pundit and former Sunderland midfielder Don Hutchison, a Newcastle fan, called the move "the biggest step backwards in the world," warning it risked destabilising a squad built to push for the top four.
Whether that scepticism proves fair may hinge on the very qualities that have followed Jaissle through his career: an unbending footballing philosophy paired with a reserve that has never much bothered with winning people over. St James' Park, a stadium not known for its patience, will be a very different test of both.