The 23-year-old England goalkeeper has signed a long-term contract at the Emirates Stadium and goes straight into the squad for Sunday’s Premier League clash against Chelsea.
Ramsdale will compete to become Arsenal’s new number one with German shot stopper Bernd Leno this season.
Arsenal had a number of bids turned down by Sheffield United earlier this summer but the championship side relented after their valuation was met.
Ramsdale has suffered back-to-back relegations with Bournemouth and Sheffield United in the last two seasons but is still regarded as one of the best young goalkeepers in England.
Ramsdale was one of England manager Gareth Southgate’s back up options at EURO 2020 although he is yet to make an appearance for his country at senior level.
"Goalkeeper Aaron Ramsdale has joined us on a long-term contract from Sheffield United," the club wrote in a statement.
"The 23-year-old, who was part of England’s Euro 2020 squad, has represented England at all levels from Under-18 to Under-21 and was Sheffield United’s player of the year last season."
Ramsdale is Arsenal’s fifth summer signing, joining the likes of Martin Odegaard, Ben White, Albert Sambi Lokonga and Nuno Tavares.
Arsenal started this season on the wrong foot, losing 2-0 to newly-promoted Brentford last week but will look to put things right against the European champions at home on Sunday.
