The Gunners swooped for the Ghanaian international on deadline day, paying his £45m fee plus ad ons taking it to £52.5m in order to complete the signing from Atletico Madrid.
He will wear the No 18 shirt and will join up with his new team-mates, becoming Arsenal’s seventh signing of the summer
Partey has been a key player in Diego Simeone’s midfield since breaking into the first team from Atletico’s academy in 2015.