Byrnes had little formal education served an apprenticeship to a joiner and builder, and pursued that occupation for a number of years.

Together with his younger brother William he invested in steam-powered cotton, wool and flour mills and pioneered steam ferry transport on the Parramatta River.

Byrnes was a leading Methodist layman and was involved with a number of charities in Parramatta including the District Hospital and the Benevolent Society.

[3][2] Prior to the establishment of responsible self-government, Byrnes was elected to the semi-elected New South Wales Legislative Council in March 1850.

Following the granting of self-government, Byrnes was elected to the first Legislative Assembly as one of the three members for the seat of Cumberland (South Riding).

In August 1867 it was commented in the colonial press that he had discharged the duties of that office “if not with any marked brilliancy, at least, with industry and considerable ability”.

[7] In 1875 Byrnes was appointed to the office of Government Valuator of resumed lands required for railway purposes.