The move represents a coup for the 2024 strugglers, who have fallen further behind their main rivals in what has been a disappointing campaign to date.
They hope that the acquisition of the man widely regarded as the sport's greatest-ever designer will enable them to become regular title challengers for years to come.
Speaking ahead of this weekend's Azerbaijan Grand Prix, two-time champion Alonso spoke of his excitement at the prospect of linking up with the 65-year-old, and admitted that the pair had made contact earlier in the season.
Addressing media in Baku, the Spaniard said: "I text him for sure, like everybody probably did, that wanted to work with him.
"I also saw him at the Monaco Historic Grand Prix when he was racing that week, and we spent half an hour chatting as well.
"We all tried to persuade him and I think that ultimately, Lawrence [Stroll's] vision, the new factory, and what Aston Martin wants for the future, together with Honda as well were probably key factors."