South Park creators Trey Parker and Matt Stone chose Obsidian to develop their RPG one year before THQ picked it up for publication.
Speaking to Ripten, THQ boss Danny Bilson said the game is entirely Parker and Stone's "vision".
"This game came to us. Matt and Trey wanted to do a great game," he said.
"They had even contracted Obsidian themselves before we came in and, I believe, there was work going on for about a year.
"They were looking for a publisher to get it involved and pick it up and drive it the rest of the way. That’s what we’ve been doing since the end of last summer; somewhere around there."
Bilson said the game is going well, with some playable sequences completed, which he described as "phenomenal" and "the funniest game ever made".
"There are sections of the game where all the voices are in and all the writing and rewriting has been done by Matt and Trey. When you get all the pieces together, it’s what everyone wants it to be," he said."
South Park: The Game is currently slated for a 2012 release, but Bilson admits THQ is willing to delay it despite the company's ongoing financial difficulties.
"It’s going to be very close," he said, explaining that development "ebbs and flows" in line with South Park creators Trey Parker and Matt Stone's schedules.
"We can’t afford to ship it until it’s perfect. Matt and Trey won’t ship until it’s their vision of this ultimate role playing game, where you’re the new kid in town and it’s like being in a South Park episode," Bilson said.
Hit the link above to read the whole interview, which includes discussion of Dark Millenium Online's new direction, THQ's approach to lay offs, and more.