The McLaren team principal is leaving to head up the Alfa Romeo/Sauber Formula 1 team.
The Italian will replace the German at McLaren.
Zak Brown is the chief executive officer of McLaren Racing.
His role begins immediately. In January, he's going to start his position at the company.
When it comes to F1's new engine regulations, the role of the chief executive will be to gradually improve the team's performance so that it is competitive when it arrives.
Industry sources say he will be in charge of the entire F1 programme, both car and engine, as well as appointing a team principal to run day-to-day operations and report to him. Frederic Vasseur is moving to Ferrari.
According to people close to him, he preferred to take a position at AUDI rather than be a replacement for Mattia Binotto.
Before joining McLaren, he was head of Porsche's successful endurance racing program.
Between 2006 and 2009, he was an engineer at the BMW-owned team.
"This is a team with a rich history in Formula 1 and an organisation I know well from my time working and living in the area."
Lando Norris, who joined McLaren in 2019, tweeted it had been "mega" to work with Seidl and added: "I've never seen our team looking as strong as it is now and some of that is credit to the work you've done."
In October, it was announced that AUDI would take over the team for its first season in F1.
The Alfa Romeo brand has provided financial support for the Switzerland-based team since the beginning of the year
As it gears up for the official entry of AUDI, the outfit will continue to race under the name of 'Sauber' in the years to come.
After leading the team to three consecutive victories in the LeMans 24 Hours and the drivers' and constructors' titles in the World Endurance Championship, he joined McLaren.
He was an important part of McLaren's revival from their all-time low at the end of last year.
Since then, McLaren have established themselves as a leading team behind the big three, won their first race in six years at the Italian Grand Prix in 2021, and have expectations of making further progress after a new wind tunnel comes on stream in the middle of next year.
His departure will be seen as a blow to McLaren, as he has made a strong impression in F1, but Brown is confident.
Brown said thatAndrea is a highly talented, experienced and respected member of the team with a strong track record of leadership and success.
McLaren's technical and operational programme will be led by a man who has been an engineering leader in F1 for many years.
He worked at Ferrari as a race engineer for more than a decade.
The head of race operations, performance director and racing director went with Alonso to McLaren at the end of the year.
He has been one of the three leaders of the team since the beginning of the year.
We are realistic about the amount of work ahead of us to move back up the grid, but I am excited and encouraged that I am in this journey with a team full of talent, experience, racing spirit and dedication