Giblin was a great reader with a retentive memory, in 1862 won a prize for the best poem on the conversion of St Paul, and about this time delivered some lectures on literary subjects.

In 1869, Giblin was elected without opposition as member for Hobart Town in the Tasmanian House of Assembly, and in February 1870 became attorney-general in the James Milne Wilson ministry.

[2][3][4] The William Crowther government which followed could do little in the conditions of the period, and when it resigned in October 1879 Giblin realised that the only way to get useful work done would be to form a coalition ministry.

In August 1884, Giblin resigned from the cabinet on account of failing health; on 7 February 1885 he accepted the position of puisne judge of the Supreme Court of Tasmania, and during the absence of the chief justice administered the government in October–November 1886.

The prominent bluff to the south of Legges Tor on the Ben Lomond plateau is named after William Giblin, as his son was a member of the survey party that explored the northern aspect of the mountain in 1907.