The 32-year-old signed the Brazilian on a three-year contract and handed the number 12 shirt.
In a media chat, Willian disclosed he is at the Emirates to win the Premier League title and European trophies with Arsenal after manager, Mikel Arteta, convinced him to sign.
He further revealed that a conversation with Arteta persuading him to join them and wants to help the club improve on their disappointing eighth-place finish in the Premier League this season.
Though, Willian’s basic salary is lower than he earned at Chelsea, when bonuses, a signing-on fee and loyalty payments over the three years are included, it will amount to £220,000-a-week or around £35m over the course of his contract.
Arsenal only made it into the Europa League by beating Chelsea to win the FA Cup earlier this month.
He said: “[I like] the way they play, everything is amazing – the stadium, and I think that with Arteta, Arsenal have a great opportunity to fight again for titles in the Premier League and in Europe so I’m very happy because of that”.
“I’m excited to start. I can’t wait to go on the pitch and do my thing to help my team-mates and to help this club to shine again. That’s what I want”.
“When I talked to [Mikel], the conversation was good; he gave me confidence to come to Arsenal. He said a lot of good things to me and that’s why I have come to Arsenal”.
Arteta said: “I believe he’s a player that can really make a difference for us”.
“We have been monitoring him for the past few months, we had a clear intention to strengthen in the attacking midfielder and the winger position [and] he is a player that gives us a lot of versatility, he can play in three or four different positions”.
“He has the experience of everything in the football world but to still have the ambition to come here and contribute to bring the club where it belongs”.
“I have been really impressed with all the talks I have had with him and how much he wanted to come”.
Gunners’ Technical director, Edu, said: “I know him very well, since a long time ago because we’ve been working together for the Brazilian national team and of course I was following him because he played for another club”.
“He has a lot of fantastic attributes as a person, as a football player of course, his character. I’m 100 per cent sure that everybody in the dressing room, the fans, myself and Mikel will enjoy having Willian in our side”.