 Söder first joined the Swedish Progress Party in 1991, but left the party in 1994, after internal struggles and instead joined the Sweden Democrats.He was elected as a substitute member of the party board in 1997, but left the board to serve as secretary of the Sweden Democrat Youth between 1998 and 2000.Between 1998 and 2002, he was a member of the municipal council in Höör Municipality for the Sweden Democrats.