Moncrieff initially worked as a freelance journalist in Dublin, writing on everything from flower shows to the conflict in the Middle East.
Upon returning to Ireland, he resumed his career as a freelance journalist, but also began working for Raidió Teilifís Éireann (RTÉ).
He started on radio with the daily It Says In the Papers, and followed this up on television by presenting The End, Good Grief Moncrieff!, Black Box and Don't Feed the Gondolas.
Also on RTÉ, Moncrieff has presented The Big 40, a celebration of forty years of Irish television, Ireland Undercover, HQ, The Holiday Quiz, and he is the voice of The Restaurant.
A non-fiction book, Stark Raving Rulers: twenty minor despots of the twenty-first century, was published in October 2004, followed by God, A Users' Guide in 2006.