Born in Cork, he was the son of James O'Hea, a barrister who was active in the Young Ireland movement and had been secretary to Daniel O'Connell.

After the style of Vanity Fair, each issue featured a colour caricature of a notable person, drawn by O'Hea under the name "Spex".

He also drew cartoons for The Nation, and created poster-sized lithographs for the Christmas issues of magazines such as the Shamrock, Young Ireland and The Sunshine.

In 1883 the conservative British journal St. Stephen's Review described O'Hea as an "out-and-out nationalist", but also as "one of the cleverest artists in the three kingdoms" who "could be making his thousands per annum if he cared to live in London, where he is well known and highly thought of;" instead he "draws his most marvellous cartoons for the most miserable of Irish comic papers."

In 1890 William Ewart Gladstone gave "a high testimony to the ability and principle of the Weekly Freeman artist" and described his pencil as "directly guided by a spirit of patriotism".