He joined
NALGO in 1975, and in 1990 he became its deputy general secretary. He was UNISON's deputy general secretary (DGS) from its formation in July 1993, when it was formed from NALGO,
NUPE and
CoHSE. He was a member of the
TUC General Council, TUC executive committee and the Trade Union Labour Party Liaison Committee. He was elected
President of the TUC for the year 2008. In July 2020, he announced his decision to step down at the end of the year.
Christina McAnea was elected as his successor in a ballot of members, in which she won 47.7% of the vote. It was announced on 14 October 2022, that as part of the
2022 Special Honours, Prentis would receive a
life peerage, sitting for the
Labour Party. On 18 November 2022, he was created
Baron Prentis of Leeds,
of Harehills in the City of Leeds. ==Public appointments==