After working as a shop assistant, bartender, storeworker, farmhand, driver, factory worker, and quarrier, he became involved in the trade unions, primarily those relating to the service sector.

[3] Later in 1993 he won the Labour nomination for the Hastings electorate, defeating Auckland Tamoana Freezing Workers' Union president Pat Weir.

Soon after entering parliament he supported Helen Clark in her successful leadership challenge to Mike Moore.

In 2005 he lost the seat in what was a large swing against the sitting Labour government in the provincial areas and returned to Parliament as a list MP.

In 2008 Barker tried unsuccessfully to regain the seat of Tukituki and for the second time was returned to parliament as a Labour list MP.

He stood in one of the safest National seats, Taranaki-King Country, in 2011 and was not high enough on the Labour list to remain an MP.