As part of the Ulster Covenant campaign against Home Rule the Northern Whig for Saturday, 25 April 1914 carried an "Appeal to British Trade Unionists to help resist Home Rule" signed by, amongst others, "Thompson Donald, Trade Union Congress delegate 1909 and 1911 – Shipwrights and Ship Constructors Society".

[9] A month after World War I ended, trade union candidates stood in three Belfast constituencies under the UULA banner during the Westminster election in December 1918.

Donald was successful in his bid for Belfast Victoria, as he was remembered as one of the organisers of the 1914 meeting against Home Rule, was a member of the Orange Order and was a Mason.

[13] Donald, Whitla and Carson, all backbenchers, were unable to live in London on their annual salaries of £400 and were financially assisted by the Ulster Unionist Party (UUP).

That July, Donald dismissed the sackings of Catholic labourers as a conflict "of Unionists and Sinn Féiners" rather than a religious issue[citation needed] after MP Joseph Devlin mentioned his concerns in the House of Commons.

[16] The four Unionist candidates who stood for seats in Belfast East on the new 52-person Parliament of Northern Ireland were elected, with Donald coming third.

[citation needed] In March 1922,[17] concerns were raised about boundaries between the two territories and whether Westminster would give parts of Tyrone, Fermanagh and Londonderry to the Provisional Government in Dublin.