During the 1970s and 1980s, Alderdice became a physician, then a psychiatrist, and then a psychoanalyst. Also, during these two decades, strife between Protestants and Catholics in Northern Ireland escalated, and Alderdice got involved in Northern Ireland politics in hopes of finding a solution to the violence. In 1978, at age 23, Alderdice, a Protestant, joined a political party that had both Protestants and Catholics in it because he thought that he could have more impact that way. It was the Alliance Party. In 1987, at age 32, he was elected leader of this party.