The 31-year-old is set to leave Chelsea on a free transfer after failing to come to terms on a new deal. Blues manager Frank Lampard had urged the club to re-sign Willian, but the board was unwilling to offer him the multi-year contract he wanted. Lampard had hoped to keep Willian because of his experience and the depth he'd provide in the Champions League next season.
Willian will be free to join the Gunners once Chelsea's Champions League campaign ends this month. The west London side is currently down 3-0 on aggregate to Bayern Munich in the round of 16.
Despite offers from Carlo Ancelotti's Everton and two clubs in Europe, Willian ultimately decided to stay in London with Arsenal. The player's agent, Kia Joorabchian, is a close friend of the club's technical director, Edu. Much-maligned center-back David Luiz, who recently signed a contract extension with the north London outfit, and oft-injured full-back Cedric Soares, who made his loan deal permanent at the Emirates, are among Joorabchian's clients.
Willian is just the latest in a long line of players to cross the Chelsea-Arsenal divide, joining Ashley Cole, Petr Cech, Olivier Giroud, and David Luiz.
He spent the past seven years at Chelsea, winning the Premier League twice, the FA Cup, and the Europa League. He appeared in all but two Premier League matches last season, recording nine goals and seven assists in 36 appearances.