Nicholson, Celtic' s legal director, took over from Dom McKay on an interim basis when the former Scottish Rugby Union chief operating officer left the club suddenly on September 10.
McKay had only arrived at Celtic Park shortly before Postecoglou and the Greek-born Australian was keen to get down to business with Nicholson and plan both transfers and changes to the football department.
"The relationship is working well," Postecoglou said. "It helps that Michael has been here and I already knew Michael, he was one of the first people I met through the process of my appointment. And he was involved in a lot of our transfer dealings anyway.
"So I have already had an established relationship, which made it easier in terms of the transition. He understands, because he has been here, the job that's ahead of us, short, medium and long term. We are very much working together to put the pillars in place that we need to.
"We have some immediate concerns obviously, that's around the football department and looking ahead to January.
"But we want to build something, not just for immediate success, but for sustainable success. So you have to get into more strategic thinking and I am working alongside Michael hand in hand with that."
Postecoglou expressed frustration with the speed of transfer incomings early in his reign but he feels there is a clear plan for the next window.
"To be fair the club has been really supportive of what I believe that we need and very supportive of the direction I want us to take," he said.
"As a manager that's all you can ask for, that the organisation, not just Michael, is really supportive of the direction that I want to take the club, in all facets, in terms of the kind of football I want to play, the kind of team I want us to be, and the kind of players I want to bring here. From my perspective, that's the key thing.
"If I keep getting that support then I am really confident we will bring in the right kind of players in January, which we need to help bolster the squad, and then have a real good foundation for what's ahead.
"Because there is no doubt this has been a major rebuild. That's not just an opinion, that's a fact. When you bring in 12 players in one window, that pretty much signifies you are building something completely new."