She was first elected as a Fine Gael Teachta Dála (TD) for the Galway South constituency at the 1957 general election. She was re-elected at the 1961 general election for the Galway East constituency and again at the 1965 general election. After boundary changes, she was elected at the 1969 general election for Clare–Galway South, where she was returned for a fifth and final term at the 1973 general election.
Hogan-O'Higgins' years as a deputy were mostly spent in opposition: Fianna Fáil was in power continuously from 1957 to 1973, and it was only in her last term (in the 20th Dáil) that Fine Gael formed a government. She was defeated at the 1977 general election, when Jack Lynch led Fianna Fáil's return to government with a large majority.
Her father, Patrick Hogan was a TD for Galway from 1921 until his death in 1936.
Her husband, Michael O'Higgins, was also a TD, as were his father, uncle and brother. She married Michael O'Higgins in 1958, one year after her election. They had nine children. They were the first married couple ever to sit in the same Dáil.