He was born at Gresham Buildings, Dollymount, Dublin, on 5 December 1879, the son of Thomas Hazleton, a draper originally from Dungannon, County Tyrone, and Bridget Rose Ryan.

[2] He was one of the founders of the Young Ireland Branch of the United Irish League, which included Thomas Kettle, Rory O'Connor and James Creed Meredith.

[4] At the 1906 general election, the 25-year-old Hazelton contested the South Dublin constituency, where he lost by a wide margin to the Unionist Walter Long,[5] a former Chief Secretary for Ireland.

However, Thomas Higgins, the nationalist candidate in North Galway, had died the night before counting of the votes commenced and was elected posthumously, thereby creating an immediate vacancy.

This time he defeated Tim Healy in a bitter contest, by 2,509 votes to 2,021,[10] but the North Louth result was subsequently overturned on petition, the reason cited being corrupt and defamatory conduct.