John Ryan Brenan was an Australian politician and an elected member of the New South Wales Legislative Assembly for 68 days in 1856.
Brenan was born into a Protestant Anglo-Irish family and trained as a solicitor.
He emigrated to Sydney in 1834 and held numerous judicial appointments including Coroner, Superintendent of Convicts and Police Magistrate. At the same time he established a private legal practice and was the solicitor for the Bank of Australasia. He owned extensive property in Camden and Maitland.
At the first elections for the New South Wales Legislative Assembly after the granting of responsible government in 1856, Brenan was an unsuccessful candidate for the two member seat of Cumberland (South Riding).
He was defeated by William Manning and Elias Weekes. However, Weekes had also been a candidate for the seat of Northumberland Boroughs and although initially defeated in that electorate, he successfully contested the result and was declared to be the member.
Unable to represent two electorates, Weekes chose to represent Northumberland Boroughs and Brenan was successful at the subsequent Cumberland (South Riding) by-election. However, his election was overturned by the Elections and Qualifications committee of the Assembly when it was discovered that voting had not occurred in Canterbury.
Brenan decided not to contest the subsequent by-election, so that the Colonial Treasurer and former Premier Stuart Donaldson, who had previously been defeated in a ministerial by-election in the seat of Sydney Hamlets, could re-enter parliament.
Brenan was unsuccessful in the Cumberland (South Riding) 1857 by-election caused by the resignation of William Manning and in the seat of Hartley at the 1858 election and he did not stand for further public office.