Oenoki was educated at and played for Shimizu Higashi High School. He won the national high school championship with his teammates including Kenta Hasegawa and Takumi Horiike. He continued his study and football at Waseda University.

After graduating from the university in 1988, he joined Japan Soccer League side Yamaha Motors (current Júbilo Iwata). When Japan's first-ever professional league J1 League started, Shimizu S-Pulse was founded in his local city. He joined the club in 1992 and re-united with his high school teammates Hasegawa and Horiike. He helped the club to win the 1996 J.League Cup, the second stage of the 1999 J1 League, and the 1999–2000 Asian Cup Winners' Cup.

He made more than 250 league appearances for Shimizu and retired after the 2002 season.

Oenoki was capped 5 times for the Japan national team between 1989 and 1990.^[1] His first international appearance came on May 5, 1989, in a friendly against Korea in Seoul. he also played at 1990 World Cup qualification.

Oenoki worked as a coach at Shimizu S-Pulse in 2003 and he was the manager of Waseda University between 2004 and 2007. Under his guidance, Waseda was promoted from the Tokyo Prefectural University League to the Kanto League Div 2 in 2004, and then to Div 1 in 2005. The club finished runners-up in the national intercollegiate championship in 2006. He acquired the S-Class coaching license that is a prerequisite to manage a J.League club in 2007. In 2008, he returned to Shimizu S-Pulse and became a manager for youth team. In July 2014, he became a manager for top team as Afshin Ghotbi successor. However the club performance is bad he resigned in July 2015.

^[1]

^[2]

• Katsumi Oenoki at National-Football-Teams.com
• Japan National Football Team Database
• Player statistics at J.League (archive) (in Japanese)  
• Manager statistics manager profile at J.League (archive) (in Japanese)