This enabled him to enter the Liverpool School of Technology, where he studied metal plate working, taking first class honours and the Bronze Medal of the City and Guilds.
In 1920, he took a leading role in a merger which formed the National Union of Sheet Metal Workers and Braziers, with Kidd initially serving as secretary of its number 2 district.
He became the union's assistant general secretary in 1923, also serving on the Executive Committee of the Federation of Engineering and Shipbuilding Trades (FEST).
Concerned that the FEST did not provide for effective action, he successfully proposed that it was transformed into the Confederation of Shipbuilding and Engineering Unions.
In addition, he served on the executive of the National Council of Labour Colleges, and taught social history to workers in his spare time.