He took part in the IRA's Border Campaign as a young man, which resulted in him being imprisoned in Mountjoy Prison for six months.

[3] However, following the failure of the campaign, he endorsed the IRA's and Sinn Féin's move towards social activism and participating in politics.

[4] He worked at the local sugar factory for 18 years, and first held political office in 1967, when he was elected to Mallow Urban District Council as a Sinn Féin representative.

During the split in Sinn Féin in 1970, Sherlock remained with the "Official" wing of the movement.

Joining the new Democratic Left party, he was elected to Seanad Éireann in 1993 (as part of an election pact with the Progressive Democrats),[6] serving in the upper house until 1997.