Michelle Smith's father taught his daughters how to swim, and Smith was first spotted by a lifeguard in Tallaght swimming pool at age 9. He suggested that Smith's father enroll his daughter in a swimming club. Smith joined Terenure Swimming Club and trained under the tutelage of Larry Williamson. Smith won the Dublin and All-Ireland Community Games at aged 9. She then won ten gold medals at a novice competition. She enrolled in the King's Hospital Swimming Club in 1980. At aged 14, Smith won ten medals at the Irish National Swimming Championships. At 14, she became National Junior and Senior Champion and dominated Irish women's swimming until her retirement in 1998.