O'Shea's climbing career began at the age of 13 when he started climbing in the MacGillycuddy's Reeks near his home-place in County Kerry, Ireland. His adventurous spirit led him to be one of the first people in Ireland to gain the Gold Gaisce - The President's Award. From here he went on to climb extensively in the European Alps and internationally. He then went on to volunteer in Kerry Mountain Rescue for 10 years.