Gahagan's early conversion to Catholicism barred him from becoming a lawyer and prompted his parents to disown him. He married a wealthy heiress, but his cruel treatment of her led to their separation. With accumulating debts, he moved to London hoping to make a living writing, acting as an editor and translating some of Pope's works into Latin. He was sentenced to execution for illegal coining. He wrote verses addressed to the duke of Newcastle and Prince George in the hopes of obtaining a pardon, but in vain.