Dee ihe na-esote paragraf a - Amụrụ na Cobh, County Cork, O'Sullivan gụrụ akwụkwọ na Cobh Community College. Ọ gụchara akwụkwọ n'afọ 1987. Asọmpi mba ụwa mbụ O'Sullivan mere bụ asọmpi Iko Mba Europe nke afọ 1990
na Split, ebe ọ gbara onye nke iri na otu na 3000 m. Agbanyeghị, O'Sullivan ka mma ngwa ngwa mgbe nke ahụ gasịrị, na Jenụwarị 26 n'afọ sochirinụ, na Boston, o setịpụrụ ndekọ ụwa ọhụrụ n'ime ụlọ n'ime 5000 m nke 15:17.28, na-ewe ihe karịrị sekọnd 5 site na ndekọ ochie. N'oge ahụ, O'Sullivan (onye nwetara agụmakwụkwọ egwuregwu) na-agụ akwụkwọ na Mahadum Villanova na US, na na World Student Games na Sheffield na July 1991, o meriri ọla edo na 1500 m na 4: 2.14, na ọla ọcha na 3000 m na 8:56.55. Na mbido afọ 1992, ọ gbara nke asaa na World Cross Country Championship.