On 25 August 2013, English side Chelsea agreed a deal to sign the Brazilian for a fee of £30 million, subject to a work permit hearing on 28 August 2013. The deal was made official on 28 August 2013 and Willian signed a five-year contract receiving the number 22 shirt.

In 2007, after coming through their youth system, Willian started playing for the Corinthians first team, where he wore the number 10. He made his league debut for the club at the age of 18 in a 1–0 victory over Juventude on 3 May 2007. His first goal for Corinthians came in a 2–2 draw against Atlético-PR on 2 August 2007. He scored both goals for Corinthians. He ended his time with Corinthians after two seasons in the first team with 37 total appearances, 16 of which came in the league, and 2 goals, which both came in the league.

On 23 August 2007, he signed a five-year contract with Shakhtar Donetsk for a transfer of €14 million. Willian's debut for the club came in a 2–1 league victory over Chornomorets Odesa on 15 September. He came on as a 57th minute substitute, replacing fellow Brazilian Jádson. His first goal for the club came on 31 October in a 4–1 victory over Arsenal Kyiv in the Ukrainian Cup. He made his European debut in a 3–0 Champions League defeat to Italian side A.C. Milan on 6 November, coming on as a 73rd minute replacement for Răzvan Raț. He ended his first season with 28 total appearances, 20 of which came in the league, and 1 goal. He helped Shakhtar to a Premier League and Ukrainian Cup double. They won the league by 3 points over Dynamo Kyiv and also beat them 2–0 in the Ukrainian Cup Final.

On 31 January 2013, Willian moved to Anzhi Makhachkala for a fee thought to be in the region of €35 million. He originally chose to wear the number 10, however due to UEFA restrictions that states a player must wear a number used in the UEFA Champions league for the remainder of the season, he was forced the wear the number 88 he had chosen at Shaktar Donetsk. After moving to Russia, Willian said he was happy to join Anzhi and wished Shakhtar Donetsk great success in the future. On his debut Willian was injured against Newcastle United in a Europa League match.
In August 2013, Following restructuring at business level, Anzhi chose to transfer list their whole squad, including new signing Willian.

As a member of the U-20 Brazil team, he made his debut in the 2007 South American Youth Championship against Chile on 7 January 2007, which Brazil went on to win. In 2007, he was also selected for the FIFA U-20 World Cup, but Brazil were eliminated in the quarter-finals by Spain.
On 10 November 2011, Willian made his senior debut for Brazil in a friendly match against Gabon.