O'Shea was educated at St Patrick's College in Wellington. In the 1960s, he later graduated from the Victoria University of Wellington.[1] After gaining his qualifications, O'Shea became a junior public servant. He would remain in the public service for the rest of his career.[2]
In this mostly symbolic position, O'Shea has been the principal adviser to governments regarding the honours and awards granted to New Zealanders, including the designing of the Queen's Service Order (1975), the Order of New Zealand (1987), and the New Zealand Order of Merit (1996), amongst other commemorative medals.[2] As part of his heraldic duties, he has also been involved in the design of coats of arms for several governors-general.[3][4] O'Shea has since been recognised with a number of honours himself due to his contributions as the specialist advisor of the honours unit to the Realm of New Zealand.[5][6]
Statant within a crown or a kea holding in his dexter claw the baton of the New Zealand Herald of Arms Extraordinary all proper.
Escutcheon
Or, the badge of the New Zealand Herald of Extraordinary (a complex Māori Koru coloured in the traditional manner proper ensigned by a representation of the royal crown also proper) with, on a chiefazure, a mānuka flower proper between two plates.