He had long been a member of the Labour party; he had twice made attempts, both in 1910, to enter Parliament for the old mid-Glamorgan division, but both were unsuccessful; but in 1918 he was elected unopposed for the new Ogmore division, and kept it safely until his death; one good reason for the lack of opposition in 1918 lay in his attitude during the war in spurring on coal production and steering the miners’ minds away from dangerous agitation. In 1924 he was’ made postmaster general in the first Macdonald ministry (and also a member of the privy council); he, like others, found he could not master the intricacies of such a new post in a moment, and occasionally the Opposition caught him unready and incomplete in his answers. In 1927 he was a member of the Simon commission sent to India to attempt unravelling the refractory problems of that country; he, in fact, was the author of that section of the report that dealt with the proposed representative assembly and the system of electing its members. After the general election of 1929 he became lord privy seal, with special responsibility for the problem of unemployment, and though he had strong proposals on the subject, which he submitted to the Prime Minister within two months of his appointment, his death (together with the unhappy crisis of the summer of 1931) put all such proposals on the shelf. He d. 13 March 1931.

There was nothing of the tub-thumper about Hartshorn; he was not a fluent speaker; what eloquence he had came as the climax of close and coherent argument. He never deluded his audience by crude denunciations of the employers, nor described, with flowery adjectives, impossible Utopias; he rather gave them food for thought, the hard facts of the situation. For this purpose he had an uncommon background of knowledge, practical knowledge of the miners’ lot, and the larger knowledge that came from intimate study of live issues of policy, whether it was of the meticulous details of the ‘sliding scale,’ or of the evidence of Blue Books and White Papers, or of the reports of royal commissions — he knew the reports of the Samuel and Sankey commissioners almost by heart, and could quote from them with ease and exactness either in talk or on the platform. He was a sane, level-headed man, a good companion, a neighbour who did many kindnesses. Under a somewhat slow and hesitant approach he concealed great powers; as a Labour leader, none was safer than he, and none abler.