The Saints midielder put in a solid series of displays for Liam Buckley's side as they strengthened their foothold at the summit of the Airtricity Premier Division
The St Patrick's Athletic midfielder picked up the award ahead of clubmates Christy Fagan and John Russell, who came second and third respectively.
Brennan joined Liam Buckley's side from Shamrock Rovers at the beginning of the 2013 season and has been pivotal for the Saints, scoring six goals in 16 league appearances. He becomes the first St Patrick's Athletic player to win the accolade since Christy Fagan, who was awarded the prize in July 2012.
It is also the first time in five years that Brennan has picked up the Player of the Month award, which he last claimed as a Bohemians player in May 2008. And despite acknowledging his own contributions, the 29-year-old was keen to direct the praise towards his team mates.
"I've felt as if I've been playing well. While chipping in with a few goals is always nice, our performances have been good and as a team we are flying at the moment," said Brennan.
"It's a great award to win as they don't come too easy. As well as we have played this season, I feel there would have been a number of my teammates in the running for this award alongside me."
He continued: "Five years is a long time to wait to win this award again, but it just goes to show how hard it is to win. This year we have a great bunch of lads who are willing to train hard every day to try and achieve our goals.
"That goal right now is to win every game we can and try and stay in the mix until the end of the season, confidence all around the club is high at the moment so long may that continue," concluded the midfielder.