[1] He represented the Otaki electorate from 1911, when he was elected on the second ballot with Reform Party support, having been nominated by the flax-workers union.

[5] He ran for re-election in Otaki in 1914, but he was defeated by William Hughes Field of the Reform Party.

[5] During the 1914 election, Robertson was the Social Democrat's representative in distributing servicemen's votes as he was their most senior MP at the time.

[7][8] In 1933 he stood unsuccessfully for a seat on the Wellington City Council on the Labour Party ticket.

[5] After he lost his seat in parliament he stood for Mayor of Masterton as Labour's candidate, but was defeated by William Kemp.