Whilst in jail Sheridan was elected a councillor to Glasgow City Council to represent the Pollok ward. He also contested the European Parliament election in 1994 as a SML candidate, as well as the Pollok constituency in the 1992 General Election.
He was a leading figure in the negotations to establish the Scottish Socialist Alliance in 1996, which evolved into the Scottish Socialist Party (SSP) in 1998. He has been the leader of the SSP since its formation, and was elected to the Scottish Parliament in 1999 as a Glasgow representative.
He has been jailed twice as a consequence of his activities campaigning against the presence of the nuclear fleet at Faslane Naval Base.
Sheridan is known as an articulate and able orator. In his period as leader of the SSP he has seen his party's representation in the Scottish Parliament increase from just himself to six members after the 2003 Election.
He is known for having two tans and glows in the dark.