Muldoon was born June 20, 1951 in Portadown, County Armagh, Northern Ireland. The son of Patrick Muldoon, a laborer and market gardener, and Brigid Regan, a schoolteacher, Muldoon grew up Catholic in the mostly Protestant town of Collegelands near a village called the Moy. As a young teenager, Muldoon studied the Gaelic language and Irish literature at St. Patrick's College, where he also began writing poetry. He also studied literature and philosophy at Queen's University in Belfast, where he met and worked with a number of prominent Irish writers who later became known as the Ulster Poets. This group of writers included Michael Longley, Derek Mahon, and Nobel laureate Seamus Heaney, who became Muldoon's tutor at the university and who encouraged Muldoon to write poetry.

In 1971, Muldoon published his first collection of poems, Knowing My Place. In 1973, he published New Weather, which was praised for its verbal virtuosity...