O'Connor is Bridges' brother-in-law.
"I wish to reaffirm to you my staunch support for Simon Bridges as Leader of the National Party," O'Connor said.
In the post, O'Connor took aim at the media.
"It is universally acknowledged that Leader of the Opposition is the most difficult job in Parliament and Simon has been persevering in that role against an unfair and unrelentingly hostile media."
He said the fact that Bridges had managed thus far in one piece was a "testament to his character".
"The media are eager to drive him out of office for his genuinely conservative principles and to make life easier for the Labour-led Government. I am determined to do all that I can to block their agenda."
He said there are bound to be "more stories in the media on this matter" in the coming days.
"It is regrettable, but once Mr Ross had chosen his course of action, there was little that anyone could do to avoid it. I am confident that we will be able to weather this turbulence and that we will emerge an even stronger and more united party going forward."
Other National MPs have also taken to Facebook to voice their support for Bridges.
Hutt South MP Chris Bishop said he was "furious" with Ross, who "deliberately [and] despicably undermined" Bridges.
"I am confident that Simon did the right thing by pursuing the leak inquiry in the first place, even though there was a lot of criticism of it at the time."
In a Facebook video, Northland MP Matt King called Ross a "rogue" MP.
"It's been a hell of a week, to be honest, for our team."
He said Ross turned out to be a "totally different man" to what he had previously thought of him.
He said anyone who is "blue-blood National" would never try and take the party down and damage it, "just purely for his hatred of Simon Bridges."
Meanwhile, Maureen Pugh – who Bridges called "f***ing useless" in a secretly recorded tape – hinted her conversation with the National Leader was slightly more intense than she had previously let on.
Earlier in the week, she said Bridges had apologised to her and she was "really happy" with how they had left things.
In response to a comment on a Facebook post Pugh made where she said she had accepted his apology, one commenter said this was "not the right response from a [West] coaster."
Pugh replied: "You didn't hear what I said to him in person!"
