Mangan joined Killorglin Cycling Club in 1952. In that year, and in 1953, he won the County Kerry Road Championship. Mangan won the 1955
Rás Tailteann aged 18; as of 2015 he is still the youngest-ever winner. In 1958, Rás won the last four stages, setting a record that still stands. Mangan also won several races at the
Irish National Cycling Championships. ==Personal life and death==