Leandro Trossard (centre) has scored seven goals so far this seasonArsenal have signed Belgium international Leandro Trossard from Brighton for £21m plus add-ons.
The 28-year-old forward's contract runs until 2027 and has the option of being extended by a year.
He has scored seven goals and provided three assists in 16 top-flight games for Brighton this season.
"He knows the league here and I think he can have an immediate impact in the team," Arsenal manager Mikel Arteta said.
The Gunners say they have submitted the required documents and hope Trossard will be available to face Manchester United at Emirates Stadium on Sunday (16:30 GMT).
"We're really happy to have him," said Arteta, who confirmed Trossard had trained with the squad on Friday.
"He's a player we have followed for a while now and the opportunity came and we have the necessity to have a player in the front line that is versatile enough to to play different positions."
Trossard, who made three appearances for Belgium at the 2022 World Cup, will wear number 19 for Arsenal.
The Gunners are top of the Premier League and Arteta feels it is "very important" to sign players who can adapt quickly.
He said: "We have to think short-term but also medium and long-term and I think he gives us all that. He's a very intelligent player.
"When you look at his career and what he has done in the last few years, he is a player who fits our way of playing for sure and we are happy to have him."
Trossard's agent, Josy Comhair, said last week the forward wanted to leave Brighton and would not sign a new contract after falling out with boss Roberto De Zerbi.
He was left out of the squad for the 3-0 home victory over Liverpool after leaving training early without permission.
