He played four seasons in the Finnish top division Veikkausliiga and won the Finnish Cup with his side FC Haka in 2005.

Viljanen was a member of the Finnish squad in the 2009 UEFA U-21 Championship.

Viljanen made his Finnish premier division debut in June 2014 by officiating the match between FC Inter and MYPA.

[1] In July he was nominated as one of the referees of the 2014 Nordic Under-17 Football Championship in Denmark.

This biographical article related to association football in Finland, about a defender, is a stub.