The Australian driver was announced as the replacement for rookie Nyck de Vries in a shock move that will see him return to the team he completed his first full F1 season with in 2012 (then known as Toro Rosso).
“There's no doubt about his driving skills, and he already knows many of us, so his integration will be easy and straight forward.
“The team will also profit a lot from his experience, as he is an eight-time Formula 1 Grand Prix winner. I would like to thank Nyck for his valuable contribution during his time with Scuderia AlphaTauri and I wish him all the best for the future.”
After two dismal seasons with McLaren, Ricciardo departed before his contract was due to end by mutual agreement, with his seat at Woking taken by fellow Australian, Oscar Piastri.
Ricciardo's return to the Red Bull as the team's third driver for 2023 sparked suggestions that he would mount pressure for the second seat at Red Bull, currently occupied by Sergio Perez, making the sooner than expected return to the grid with AlphaTauri even more of a surprise.
“I'm stoked to be back on track with the Red Bull family!” Ricciardo said.
While Red Bull Racing leads the Constructors' standings by more than double next-best Mercedes, AlphaTauri sits tenth and last with only two points after 12 rounds.
The 2023 Hungarian Grand Prix takes place on July 21-23.