AlphaTauri has announced that Tost will step down as team principal at the end of the 2023 season, with Mekies due to return to the Italian squad in his place - and will join the team at an undisclosed date.
In addition, former FIA executive director Peter Bayer will join AlphaTauri later this season as its CEO, with his remit to oversee the strategic direction of the team across both its facilities in Italy and the UK.
Tost had been in charge of the team since 2006, having been appointed by Red Bull GmbH once it had completed its takeover of the Minardi team at the end of 2005.
The Austrian oversaw two victories at the squad in its Scuderia Toro Rosso and AlphaTauri guises, both at Monza, as Sebastian Vettel secured victory in a wet 2008 race and Pierre Gasly doubled the Faenza team's tally in 2020.
However, the recent downturn in performance at the team had placed Tost under the microscope, and his recent comments regarding a lack of trust in the AlphaTauri engineers had not gone down particularly well within the camp.
“First of all, I would like to thank Dietrich Mateschitz, who gave me the incredible opportunity to be team principal of Scuderia Toro Rosso and Scuderia AlphaTauri for the past 18 years," Tost said, who will retain links with the team on a consultancy basis.
"It has been a true privilege to lead the team for such a long period and a great pleasure to work with so many motivated and skilled people, who share my passion for Formula 1.
"At 67 years old it is time to hand over and with Peter as new CEO and Laurent as team principal, we found two very professional people, who will bring the team to the next level."
Mekies had served as a race engineer and head of vehicle performance at Toro Rosso, having been with the team during its Minardi days, before departing for the FIA.
The Frenchman worked for the motorsport governing body as safety director and deputy race director, and had been touted as a successor to the late Charlie Whiting, before moving to Ferrari as sporting director in 2018.
"Firstly, I’d like to pay tribute to Franz for the great job he has done over almost two decades in charge at Faenza," Mekies stated.
"I wish him well for the future and I know that both Peter and I will rely on his input and advice in times to come. Looking forward, I am honoured to take on the role of team principal and to return to the team where I spent a large portion of my early career.
"AlphaTauri has all of the ingredients necessary for greater success in the future and in tandem with Peter I’m looking forward to making that happen."
For his part, Bayer departed the FIA midway through 2022 having served as the secretary general for sport at the governing body before adding his F1 executive director role to the mix in 2021.
“I would also like to thank Franz for his dedication to Scuderia AlphaTauri and its predecessor, Scuderia Toro Rosso," Bayer said.
"It is a great privilege for me, too, to take on the role of CEO at the team and working alongside Laurent. AlphaTauri has a fantastic team of people and great infrastructure in Faenza and in the UK.
"I am very much looking forward to building on those key elements to increase performance, on and off track, and to bring the team even more success in the coming years."
