Okazaki was born in Takarazuka on April 16, 1986. After graduating from Takigawa Daini High School, he joined J1 League club Shimizu S-Pulse in 2005. He played many matches from 2007. The club won the 2nd place in the 2005, 2010 Emperor's Cup and 2008 J.League Cup. In January 2011, he moved to German Bundesliga club Stuttgart and played in 3 seasons. In 2013, he moved to Mainz. He scored 27 goals in 2 seasons. In 2015, he moved to English Premier League club Leicester City. In first season, the club won the Premier League champions. He played for the club in 4 seasons. In July 2019, he signed with Spanish Segunda División club Málaga CF. However, Málaga canceled its contract, since the team was unable to register him as his wage demands exceeded its maximum budget spend as permitted by the league. In September 2019, he signed with Segunda División club Huesca. The club won the champions in 2019/20 season and was promoted to La Liga.