Seppänen was born in Oulu, and began politics by joining the Social Democratic Youth. In 1974 he joined the Communist Party of Finland.[1] He belonged to the more Eurocommunist majority of the party (as opposed to the Taistoist Neo-Stalinist minority). In 1989 Seppänen opposed merging the Communist Party into the new Left Alliance (Vasemmistoliitto), criticizing the procedure as undemocratic.[2] Nevertheless, Esko Seppänen worked in the leadership of the new party until 2001.[3]
Seppänen has a bachelor's degree in business studies (1971). He worked as journalist at Yleisradio in 1970–1987.