Brennan was praised for his "nonchalant delivery" of thanks to the "girlfriends and boyfriends of the players" after St Vincent's defeated Castlebar Mitchels in the 2014 All-Ireland Club Championship Final at Croke Park (a speech delivered in front of a live television audience). However just over a year later, Brennan wrote an op-ed for the "Irish Independent" arguing against the legalisation of same-sex marriage in that year's Marriage Equality referendum, which was ultimately carried in a 62% to 38% popular vote. His stance was criticised by others, including fellow GAA star Conor Cusack.