[1] Barr became a shop steward in 1942, and by 1948 was a member of the National Union of Sheet Metal Workers and Braziers's Executive Committee.

[2] He stood unsuccessfully for the CPNI in Belfast Bloomfield at the 1953 Northern Ireland general election, taking only 11.8% of the votes cast.

Barr was appointed to the Northern Ireland Economic Council, but resigned in 1973 in protest at the introduction of internment.

[1] Barr opposed the Ulster Workers' Council strike of 1974, and worked with Jimmy Graham to organise a march to demonstrate this.

General Secretary of the TUC Len Murray led the march, into the Port of Belfast, with Barr.