He soon became involved in trade unionism, and was elected as checkweighman of his local pit.
[1] Around this time, demarcation disputes between the AMMW and the Lanarkshire Miners' County Union (LMCU) led the union to leave the Scottish Miners' Federation (SMF).
The SMF sent Robert Small of the LMCU to attempt to found a rival union in West Lothian, and he attempted to persuade Doonan to lead it, but Doonan refused, and the AMMW later rejoined the SMF.
[2] In 1912, Doonan was elected as secretary and agent of the AMMW, after the union's executive decided that he would be the only candidate put forward for a vote.
[1] From 1929 until his death, he was president of the National Union of Scottish Mineworkers,[4] and he also served on the executive of the Miners' Federation of Great Britain.