Partey joined the Gunners from Atletico Madrid on transfer deadline day after the English club activated his £45 million release clause.
The 27-year-old will wear the number 18 shirt at Arsenal, and will reportedly be on a £250,000 per week wage.
The Ghanaian had been the target of transfer speculation all through the summer, having been linked with several elite clubs.
However, it was Arsenal who won the race for his signature after paying the midfielder’s release clause in full.
Having played for Ghana in international friendlies against Mali and Qatar, Partey flew to his new club for the first time.
The midfielder was unveiled on Tuesday, as he posed for photos in Arsenal’s home and away kits.
Meanwhile, Partey has overtaken Michael Essien as the most expensive Ghanaian footballer of all-time following his move to Arsenal.