[7] His debut for the club came on 15 September in a 2–1 league victory over Chornomorets Odesa, where he came on as a 57th-minute substitute, replacing fellow Brazilian Jádson.

[citation needed] Willian scored his first goal for the club on 31 October in a 4–1 victory over Arsenal Kyiv in the Ukrainian Cup.

[citation needed] He made his European debut on 6 November in a 3–0 Champions League defeat to A.C. Milan, coming on as a 73rd-minute replacement for Răzvan Raț.

He played in the Super Cup penalty shoot-out victory over Dynamo Kyiv on 15 July, being replaced by Brandão after 46 minutes.

[citation needed] Willian's first goal of the season came in a 6–1 Ukrainian Cup round of 32 victory against Dniester Ovidiopol on 15 August.

[15] He made an appearance in Shakhtar's 1–0 extra time defeat to Spanish side Barcelona in the UEFA Super Cup on 28 August, being replaced by Julius Aghahowa in the 90th minute of the match.

[16] On 17 September, he netted the second goal in a 4–1 win against Belgian side Club Brugge in a group stage match in the Europa League.

[18] Willian started the season with a goal in Shakhtar's emphatic 7–1 victory against Tavriya Simferopol in the Super Cup on 4 July.

[30] Shakhtar opened the season with a 2–0 win against Metalurh Donetsk in the Super Cup, however Willian failed to make the squad for the match.

[37] After moving to Russia, Willian said he was happy to join Anzhi and wished Shakhtar Donetsk great success in the future.

[39] In August 2013, following financial restructuring, Anzhi chose to transfer their whole squad, including recent signing Willian.

[41] The deal was made official on 28 August 2013 and Willian signed a five-year contract, receiving the number 22 shirt.

[52] In extra time in a League Cup semi-final against Liverpool on 28 January 2015, he took the free-kick which was headed in by Branislav Ivanović to put Chelsea into the final.

[53] On 1 March, Willian was selected to start against Tottenham in the 2015 League Cup Final at Wembley Stadium, a match which Chelsea won 2–0 to win the trophy for the fifth time.

[63] On 22 April 2017, Willian scored twice in Chelsea's 4–2 FA Cup semi-final victory over rivals Tottenham at Wembley Stadium.

[64] On his 200th appearance for Chelsea, Willian scored twice and won two penalties as the Blues beat Qarabağ 4–0 at Baku National Stadium on 22 November.

[65] In his next appearance, Willian came off the bench to score his first Premier League goal of the season, to rescue a point for Chelsea in a 1–1 draw against Liverpool at Anfield.

[66] Willian scored his first goal of the season, coming off the bench to complete a 4–1 come-from-behind win at home to Cardiff City on 15 September.

[67] On 27 January, Willian, on his 550th club appearance, netted a brace in a 3–0 home win against Sheffield Wednesday in the fourth round of the FA Cup.

[79][80] On 9 May, Willian scored his only goal for Arsenal in a 3–1 home league win over West Bromwich Albion, sealing the Baggies' relegation to the EFL Championship.

[89] On 19 March 2023, in the FA Cup quarter-final against Manchester United, Willian received a red card for using his hand to block a shot from Jadon Sancho in the 70th minute, after a VAR check.

[90][91] In July 2023, Fulham confirmed Willian had signed a new one-year deal with the club, keeping him at Craven Cottage through the 2023–24 Premier League season.

[citation needed] On 10 November 2011, Willian made his senior debut for Brazil in a friendly match against Gabon.

[100] He came on at half-time in extra time of the round of 16 match against Chile in Belo Horizonte for his Chelsea teammate Oscar, and took a penalty in the shootout which he put wide of the goal, although Brazil nonetheless advanced.

[101] At the 2015 Copa América, Willian assisted Roberto Firmino's decisive goal in the 2–1 win over Venezuela in Santiago, a result which sent Brazil into the quarterfinals as group winners.

[102] On 5 May 2016, he was named by Brazil manager Dunga among the 23-man list for the Copa América Centenario to be held in the United States.

During the game against Premier League champions Leicester City, his teammates Diego Costa and Eden Hazard dedicated their goals to Willian and his mother.

[120] In 2018, Willian and his teammate David Luiz acquired Babbo, an Italian restaurant located in Mayfair, London.