[4] Asquith became Prime Minister in 1908 and in January 1909 he appointed Tennant Parliamentary Secretary to the Board of Trade.

He faced two opponents: R. W. Foulis of the Labour Party, and the 1911–1918 Haddingtonshire MP John Deans Hope.

With two incumbent Liberal MPs contesting one seat, Hope's receipt of the coalition coupon secured his victory, with 54% of the votes.

[7] Tennant also unsuccessfully contested Glasgow Central in 1923[8] but never returned to the House of Commons.

During his time in Parliament, Tennant supported a number of progressive measures such as worker's compensation,[9] minimum wage provisions,[10] school medical inspections,[11] factory inspections, and unemployment insurance.