Marjorie L. Byrnes is an American politician and attorney from the state of New York.

A Republican, Byrnes represented the 133rd district of the New York State Assembly, covering Livingston County and other areas to the south of Rochester, from 2019 to 2024.

[3] After her retirement from the court system in 2017, Byrnes became a Caledonia Village Trustee.

[1] In 2018, Byrnes announced that she would launch a primary challenge to Republican incumbent Joseph Errigo, who had been selected by Republican leadership for the 133rd district in 2016 following Bill Nojay's suicide.

[4] That November, Byrnes defeated Democrat Barbara Baer with 55% of the vote.