Binotto will join on August 1st as Chief Operating and Chief Technical Officer at Sauber Motorsport, the Swiss-based entity that currently competes as Sauber and will become the factory Audi team in 2026.
Audi said he would have "responsibility and accountability for the operative management and sporting success of the racing team."
Hoffmann was previously chairman of the Boards of Directors of all Sauber companies while former McLaren principal Seidl was CEO of Sauber Motorsport.
"I am delighted that we have been able to recruit Mattia Binotto for our ambitious Formula 1 project," said Audi CEO Gernot Doellner in a statement.
"With his extensive experience of more than 25 years in Formula 1, he will undoubtedly be able to make a decisive contribution for Audi."
Swiss-educated Binotto joined Ferrari in 1995 and was appointed principal of the Italian team in 2019.
He resigned in November 2022, after another disappointing season for the sport's oldest and most successful team, and was replaced at Maranello by Fred Vasseur, who was previously at Sauber.
Seidl was appointed in December 2022 as Vasseur's replacement but the Swiss team have endured speculation about Audi's intentions and the possibility of terminating the project.
Audi, which is making its own F1 power unit in Neuburg in Bavaria and said last March it would take 100% ownership of Sauber, declared in Tuesday's statement that preparations were "going full speed ahead".
The carmaker said the decision to bring in Binotto was part of a realignment to ensure the autonomy and independence of the project.
"Our aim is to bring the entire Formula 1 project up to F1 speed by means of clear management structures, defined responsibilities, reduced interfaces, and efficient decision-making processes," said Doellner.
"For this purpose, the team must be able to act independently and quickly."
Sauber are the only team yet to score a point in 13 races this season, with China's Guanyu Zhou and Finland's Valtteri Bottas facing an uncertain future beyond 2024.
The Swiss team have already announced the signing of German driver Nico Hulkenberg from Haas and have been chasing Ferrari's Carlos Sainz, who is being replaced by seven-times world champion Lewis Hamilton next year.
The likelihood of Sainz joining Audi appeared to have waned recently, given uncertainty about the 2026 engine and Sauber's lack of form, with Renault-owned Alpine also increasingly interested.
Alpine have also under-performed this season, however, and recently brought in former Renault team boss Flavio Briatore as a consultant.
