After graduating Takigawa Daini High School in 2004, Okazaki signed full professional terms with Shimizu S-Pulse the following year.

He continued his promising goalscoring in the 2009 and 2010 seasons and, in January 2011, was signed by German side VfB Stuttgart of the Bundesliga.

Okazaki became the most prolific Japanese player in Bundesliga history on 13 September 2014, scoring his 27th and 28th league goals in Mainz's 3–1 win over Hertha Berlin.

[12] On 26 June 2015, Okazaki moved to Premier League side Leicester City for a fee believed to be in the region of £7 million, subject to obtaining a work permit.

On 19 December 2015, Okazaki scored the winner in a 3–2 win over Everton at Goodison Park, to ensure that Leicester City topped the table at Christmas.

[14] On 10 January 2016, Okazaki scored Leicester's second goal in the FA Cup clash at White Hart Lane with Tottenham Hotspur despite drawing to a Harry Kane penalty in the 90th minute.

[18] He scored his first league goal of the season in a 3–1 win over Crystal Palace on 22 October 2016, earning him Man of the match and achieving an 84.8% pass success rate, more than any other Leicester player.

[24][25] However, Málaga canceled its contract with Okazaki after just 34 days, since his wage demands exceeded its maximum budget as permitted by the league.

[26] On 4 September 2019, the free agent Okazaki signed a one-year contract with Segunda División side Huesca.

On 25 July 2020, after scoring 12 times as his side achieved promotion to La Liga, Okazaki renewed his contract for a further year.

[31] On 20 January 2009, he scored his first goal for Samurai Blue in the team's opening 2011 AFC Asian Cup qualifier against Yemen.

[31] On 8 October 2010, Okazaki scored as Japan beat Argentina 1–0 in friendly match to record its first ever win over the 1978 and 1986 world champions.

[31] Okazaki finished as top goalscorer in the Asian section of qualification for the 2014 FIFA World Cup with eight goals.

[36] Okazaki was included in Japan's squad for the 2015 AFC Asian Cup and scored in a 4–0 defeat of Palestine during the group stage.