Born in Bristol, Jarman went to sea when he was fourteen, and soon joined the Royal Navy.
He became involved in the National Union of Seamen (NUS), becoming its national organiser, and then its district secretary, successively in the Bristol Channel, Mersey, North East Scotland and then Scottish districts.
[3] He also joined the General Council of the Trades Union Congress, and was president of the Seamen's Section of the International Transport Workers' Federation.
[2] Jarman was also active in the Labour Party, and served on its National Executive Committee for four years.
At the 1935 United Kingdom general election, he stood unsuccessfully for the party in Birmingham Yardley.