The 27-year-old revealed on Wednesday that he would be leaving the 20-time English champions during this summer's transfer window.
Girona have now been confirmed as Van de Beek's new club, and the midfielder will have the chance to feature in the Champions League for the La Liga team during the 2024-25 campaign.
Transfer expert Fabrizio Romano has reported that Girona will pay just €500,000 (£422,000) for the midfielder, although the add-ons could take the deal to €15m (12.7m).
Van de Beek, who spent the second half of last season on loan at Eintracht Frankfurt, leaves Man United having made 62 appearances since arriving from Ajax in 2020, managing just two goals and two assists in the process.
Van de Beek completes switch to Girona
"Donny van de Beek has completed a permanent move to Girona in La Liga," read a statement from the 20-time english champions on Thursday afternoon.
"The midfielder has thanked the Reds fans for their warmth and support during his time at Old Trafford, which started when he signed from Ajax in 2020.
"Everybody at United would like to wish Donny the very best of luck in this next chapter of his career."
Van de Beek took to social media on Wednesday to thank the "Manchester United family" for their support during his time at Old Trafford.
"Dear Manchester United family, today is a memorable day as my adventure at the club comes to an end," he posted on his official Instagram account.
"I want to thank you all for your support throughout the years. From the moment we arrived at Manchester United, we felt extremely welcome and we are grateful for that.
Van de Beek struggled to make his mark at Old Trafford
"Thank you to everyone at the club for making us feel at home. A special thanks to all the fans that made these years unforgettable.
"Besides the football, the birth of our two children here ensures that Manchester will always have a special place in our hearts. Good luck to everybody, we'll meet again."
On their official website, Girona posted: "Donny Van de Beek will be a new player for Girona FC for the next four seasons, until 2027-2028. The club and Manchester United have reached a transfer agreement for the Dutch midfielder.
"The new red-and-white footballer is a very talented midfielder who stands out for his game vision, ability to score goals and his ability to create scoring opportunities for teammates. In addition, he is a versatile player who can adapt to different positions."
Van de Beek made 36 appearances for Man United during his first campaign at the club, but he found it difficult to show his best form for the English giants.