The IOG, an independent charity seeking to increase government effectiveness, was seen by the RTPI as an ideal neutral body for the initial meeting.
The meeting included representatives from the RTPI, British Property Federation (BPF), Friends of the Earth, the Campaign to Protect Rural England (CPRE), the Town and Country Planning Association, the Home Builders Federation (HBF), and the National Trust.
A civil servant from the Department For Communities and Local Government attended the meeting.
RTPI head of marketing and communications Tino Hernandez said: "It shouldn’t be seen as the RTPI muscling in.
"So we looked for an independent chair in the form of the IOG.
"We felt it was helpful with all the hostility out there - with a different story in the national press every day - to try and bring people together in a non-threatening environment."
"There will be more meetings planned."
CPRE chief executive Shaun Spiers said: "There may well be some unlikely alliances as a result of these talks. Certainly the BPF has some good points to make on brownfield land."
The NPPF consultation ends on October 17.