Commenting on his award, O'Brien reflected on last month's four games and on his own development in the Leinster Academy.
"It's always good to get these type of awards, being recognised by the supporters and everyone else - your team-mates around you. So it's a great honour to get it and I'm absolutely delighted," he told Leinster TV.
"We stuck in there against the Scarlets (at the start of the month) and got the draw in the end. We let ourselves down a bit in that game, but we made up for it in the weeks to come.
"Clermont away was a big game. I still think we could have won that game. We did well to get a point out of it, it's not easy going over there. They're a tough side, so we were happy enough to take a point from it.
"(The Fever in the Aviva) was a great game. We knew exactly what we had to do that day. We really fronted up, took the game to them and put in a good performance. There were a lot of fans there that day and we owed it to them.
"(The Ulster fixture) was a massive game for us in the Magners League, to get us back in the running.
"It's not an easy place to go up to and win in Belfast. Conditions usually aren't good and the crowd are very noisy, they really get behind the Ulster boys.
"But we stuck to our game-plan. We said before the game not to panic and just do the simple stuff and we came out the right side of (the result)."
The 23-year-old added: "The Leinster Academy is a massive thing. It really helped me, especially mentally and physically. It gave you a great insight into what the demands are on a professional rugby player.
"The lads that have come through recently, Dominic (Ryan) and Rhys (Ruddock), they are there on our heels now. It's good to have that competition there, they can fill in for you at any time.
"The likes of Eoin O'Malley and Fergus McFadden in the backs too. O'Malley's been unlucky with injuries, but Ferg has been consistently playing well every chance he's got.
"They are all good lads, they all know what Leinster's about and they all really want to win."
To vote for your Leinster Bank of Ireland Player of the Month for January, simply email firstname.lastname@example.org, explaining which player you want to vote for and why. Everyone who nominates a player is in with a chance to win a gift voucher.