Ó Caoláin's victory in 1997 made him the first member of Sinn Féin to be elected to the Dáil since 1957, and the first to actually take their seat since 1922.

[2][3][4] His election, which paralleled the signing of the Good Friday Agreement in 1998, is cited as the beginning of Sinn Féin's involvement in the formal national politics of the Republic of Ireland.

[2] Ó Caoláin served as Leader of Sinn Féin in Dáil Éireann from 1997 to 2011 and Chair of the Committee on Justice and Equality from 2016 to 2020.

Ó Caoláin was a Sinn Féin delegate at the Forum for Peace and Reconciliation in Dublin in the mid-1990s.

[8] He was also a member of the Sinn Féin negotiations team during the talks which led to the Good Friday Agreement in 1998.