The Brazilian’s contract with Chelsea expired after their Champions League defeat by Bayern Munich last Saturday.
Willian, who turned 32 on Sunday, has signed a three-year deal that will see him earn around £100,000 a-week, although that could rise with appearance and bonus clauses.
In seven seasons at Chelsea, he won the Premier League twice, the FA Cup, the Carabao Cup and the Europa League, but he is convinced he can add to that collection with the Gunners.
“I decided [to join] because Arsenal are one of the biggest clubs in the world. They have a new project with Mikel Arteta,” said Willian. “I think this club deserve to shine again and I want to be a part of this project — to be a part of the Arsenal family is amazing. I’m very happy to do that.
“I come to try to win trophies, because this club deserve to win again, and I think you have to do the best as possible to win every game.
“[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.
“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.”
Arsenal’s decision to sign Willian at his age has come under scrutiny, but Arteta explained the forward has been a long-term target of his.
The Brazilian adds experience to Arsenal’s young squad, while he is also able to play on either flank or through the middle.
“I believe he can really make a difference for us,” said Arteta. “We have been monitoring him for the past few months. We had a clear intention to strengthen in the attacking midfield and wing positions [and] he is a player that gives us a lot of versatility. He can play in three or four different positions.”
Arsenal are keen to strengthen their squad further this summer and technical director Edu is hopeful more additions will arrive.
“It will take time, but with Willian, we’ve started a big process,” said the Brazilian.
“We’ve identified the needs in the squad and he’s the one to start to rebalance the squad as we want to.”